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Eberspacher Fuel supply Faults 1.
Often the only fuel related problem considered for Eberspacher problems is running out of fuel but there are many other reasons that are easily overlooked.

Although there pages are for Eberspacher heaters Webasto use a similar fuel supply system so much of the general advice will also apply to Webasto heaters.
Eberspacher heaters use a pulsed fuel metering pump to supply tiny spurts of fuel, about 0.02ml per pulse, to the heater. The pump is pulsed by the Electronic Control unit (ECU), each time the pump pulses the solenoid makes a loud "tick". The pulse rate and pump setting determine how much fuel is supplied, there is no carburetter.
Fuel is drawn by suction from the fuel supply up to the pump.
Fuel flows into the combustion chamber where it is vaporized and mixed with air from the combustion air intake pipe and burnt.
The hot exhaust gasses pass through the inside of the heat exchanger before venting through the exhaust pipe.
It is important that pumps and fuel pipes are correctly installed as many faults can be caused by incorrect installation. There are too many details to cover here, full details are in the manuals.
Pipe lengths etc quoted here generally apply to D2 D4 and some similar heaters, check manuals for confirmation on other models.
Lower down this page shows fuel volume tests, pump testing and disassembling.
Fuel Problem page shows details of our practical fault finding when we had fuel problems on our own heater.
We welcome feedback and any additional advise you can add to these pages.
Eberspacher recommend regardless of the season, run the heater every month for a minimum period of 15 minutes which will ensure that the fuel in the pump and lines to the heater does not gel and solidify. We usually only run ours once or twice during the Summer but we run on kerosene.

Fuel types and suitability.

Fuels suitable for Eberspacher diesel heaters.
We have no expertise on fuel types so I am grateful for the specialist advice we received on suitable fuels for Eberspacher heaters.
Most fuel sold at the pumps in the UK is winterised from September onwards and therefore should be OK for winter use, untreated fuel will wax up at relatively mild temperatures.
For all fuels good housekeeping is essential, modern fuels do not store like they used to.

Road diesel - specification BS EN 590, often referred to as white diesel or Derv, very expensive.
Red diesel - This is actually Gas Oil.
  Before January 2011 'red diesel' was normally High Sulphur Gas Oil (also called 35 second oil, household heating oil).
     This was mainly used for agricultural and off road plant.
  From January 2011 fuel regulations changed so supplies now should be:
     Ultra Low sulphur Gas Oil (ULSGO) with up to 7% bio for use in all off road machinery.
     Ultra Low sulphur Gas Oil (ULSGO) with no bio fuel added, intended for use in Inland waterways and marine estuaries.
     However there is no guarantee if you own a boat that you wont be supplied the 7% bio fuel.
     It is now illegal to supply or use high sulphur gas oil on the inland waterways, it is still used for sea going boats.
Kerosene (Paraffin) - Premium Kerosene is known in the UK as Paraffin. Earlier manuals list paraffin and it is suitable.
Domestic central heating oil - There are two types of domestic heating oil, 28 and 35 second.
Standard Kerosene to BS2869 Class C2 is a heavier distillate than Paraffin. Also known as 28 second fuel, this is a lighter alternative to standard heating oil (Gas Oil) and burns much more cleanly with low sulphur content.
We are now running our own Eberspachers on 28 second fuel (see below).
35 second oil is High Sulphur Gas Oil as mentioned above. In Germany it is sold as Heating oil EL.
Biodiesel, also called FAME (fatty-acid methyl ester), is made from animal fats or vegetable oils.
The table below shows Eberspacher bio diesel compatibility, if you are unsure about suitability do not use bio fuel.

There are no problems using red diesel or gas oil but you may still find old forum articles describing problems.
The causes were investigated and solved in the Eberspacher technical report bulletin mentioned earlier.
Essentially Eberspachers will run on all of the fuels described provided there are no other issues.

Which fuel do we use?
After problems when we bought some bad red diesel we tried Kerosene, standard 28 second central heating oil.
At that time the heater was very close to needing a 2000 hour service and was smoking.
As soon as we changed there was a significant improvement, it burns cleanly with virtually instantaneous starting even in cold conditions. The smoking stopped and despite running on lowest heat setting most of the time for about a further 3500 hours the D2 has not shown any signs of needing a service. Derek highly recommends Kerosene.
An Eberspacher technical representative told us that the Ultra Low Sulphur Marine Gas Oil burns almost as clean as premium kerosene (paraffin) so he advises it is not worth fitting a separate tank for kerosene.
It may be difficult to find a kerosene supplier for small quantities, most deliver and specify at least 100 liters.
We found a hardware store in Bridgnorth Shopshire, W Powell & Son, who have regular deliveries and sell it in small quantities.
If you find other central heating oil suppliers who can sell in small quantities tell us and we will list them here.

Pump Mounting.
Pump must not be mounted less than 15 degrees from horizontal as it can trap air bubbles.
One users pump was mounted horizontally by a professional installer, it failed mechanically after two seasons light use. It should be mounted between 15 and 35 degrees from horizontal with the outlet higher than the inlet. Eberspacher recommend mounting about 30 degrees to allow for vehicles parking on a slope or for boats to tilt from horizontal. The pump can also be mounted vertically, the amount of fuel pumped will be slightly more.

Pump Ventilation.
Some users ask if the pumps can be mounted in foam or similar materials to reduce noise. This has been done successfully but under some fault conditions continuous power can be supplied to the pump and it can become very hot. If it was completely encased there would be no easy way to dissipate that heat so Eberspacher do not recommend it.

Reducing Pump Noise.
The clicking of the pump can be reduced by fitting one of the newer rubber clamps in place of the older type clamp. (see Buying advice pages).
Metal fuel pipe can transmit this noise throughout the boat though direct contact or via the fixing clips. Fit the pipe inside cheap 6mm internal diameter hose and clip that.
Mount the pump on something solid and use rubber connections.
Personally I like to hear the clicking as it tells me what heat setting the heater is using.

Water in diesel fuel.
Diesel fuel will always contain some water when sold. As the fuel level or temperature changes air enters the tank through the vent, condensation then forms when the air cools increasing the water in the tank.
The water– fuel interface at the tank bottom is an environment that encourages biological growth which can clog filters and prevent fuel flow to the heater.
Diesel floats on top of water so pickup pipes should not reach the bottom of the tank. Even then as the water sloshes about it can sometimes reach the end of the pipe and be picked up and cause intermittent and puzzling flame outs.
If water is found in the fuel siphon it off from the lowest point of the tank until clear fuel is siphoned up.

Fuel Degradation.
Diesel fuel starts to deteriorate the moment it leaves the refinery. As it ages during storage, it creates particles and a black sludge that accumulate in the tank. The diesel visibly darkens.
Debris can be disturbed when new fuel is added or when fuel sloshes around in the tank.
The cetane value of the fuel also drops as it ages and can drop so low it will no longer ignite in the heater.
More information is in the Eberspacher technical bulletin 281,  click here to view.

Priming the fuel supply.
If the fuel pipes are empty the pump has to purge the air from them before fuel can reach the heater. With a thin pipe this often takes two start attempts, with a larger or far longer pipe it can take 5 or more restarts and up to 30 minutes to start.
Manual priming by dabbing temporary wires on a battery can be done but it can take a lot of pulses. As a comparison we estimate one start attempt on a D1LC can give over 300 pulses. An alternative idea is to use a car trafficator relay to pulse the pump.

Cold weather.
Fuel thickens as the temperature drops, if it combines with debris in the fuel filter it can restrict the fuel flow.
Any water trapped in the pump or filter can freeze and block the fuel feed and seize up the pump.
Water can be trapped in the exhaust pipe and freeze which blocks the exhaust gas flow. This can be a problem on boats where the outlet pipe is higher than the heater so condensation cannot drain. Also water may enter the exhaust from the outlet, either when the boat keels over or in large waves.
Some fuels do not perform well at low temperatures.

Fuel flow and air / fuel leaks.
With transparent fuel pipe tiny air bubbles are usually visible in the fuel as it pulses towards the heater which can be a very useful diagnostic check on fuel flow.
Dereks calculations on 1.5mm internal diameter piping show fuel moves just over a cm per pump stroke giving the bubble spacing. These bubbles are created by the pump action and are present even if there are no air leaks. Despite a lot of considering we are still not sure why they are produced. If anyone can explain what produces them please let us know. If there are a lot more bubbles than those shown in the picture it can indicate an air leak. However we have noticed it does take a long time for bubbles to drop to this amount and size after the pump has been primed, it can take quite a few successful starts, the bubbles gradually diminish. Larger bubbles can be due to a serious air leak but are more often caused by lack of fuel.
If the pipe is disconnected fuel spurts out quite strongly, if it just trickles out there is a problem. The small quantity of fuel pumped, 0.02ml per stroke means small air leaks in the pipe before the pump can reduce the amount of fuel pumped.
The pipe before the pump is under suction so no fuel will leak out to indicate problems.
Leaks in the pipe between the pump and heater can result in fuel leaking.
Usual causes are holes in the rubber connecting pipes or badly sealed joints. If the rubber connecting pipe is leaking renew it together with the clamps, just tightening the bolts is often unreliable and the fault reappears.
We have found clamps have to be very tight to give a good seal but don't overtighten and sheer the bolts.
Tip - New jubilee type clips can be extremely stiff and need so much turning torque the metal pipes on the pump and heater can bend. I put the new clamp on the shaft of a screwdriver and tighten it down using a socket set until it is smaller than the rubber tube, then loosen it off again. That way it is much easier to tighten when fitted on the pipe.
Rubber connecting pipes with too large internal diameter can also give poor seals.
Fuel pumps come in 12v and 24v versions as well as several different supply rates including 1 - 3 kW and 3.1 - 5 kW.
The fuel inlet is at the end furthest from the electrical terminals.
Pumps are adjusted during manufacture to deliver the correct amount of fuel for each model so pumps from a different model are not interchangeable. However by carefully altering the spring tension sometimes pumps can be adjusted enough to match other models. One method is to adjust the small nuts, make sure they are secure so cannot undo with vibration.
Any change will require several fuel volume tests. The adjustment range is limited. Do not expect a 3.1 - 5 kW pump to adjust to match lower heat pump versions.
The D2 and D4 use the same pump which is marked 1 - 4 kW. Diesel and Petrol heaters use the same pumps.
Note these pumps need the power to be pulsed on and off to work.
Pumps are not polarity sensitive so electrical connections can be either way round.
Pumps use the fuel as lubricant for the moving parts.
Testing and disassembly details are on this page. We also include some test results using incorrect pumps.

Fuel filter.
Unscrew the 17mm nut on the fuel pump inlet.
(Photos of the fully disassembled pumps are on this page.)

Badly neglected filter with its replacement.
More fuel filter pictures are on Servicing pages.

If the nut is tight use two spanners on the inlet pipe otherwise the complete end may rotate relative to the body, breaking the seal.
A clogged fuel filter can restrict the fuel flow causing non starting or flame-outs.
It may need a pointed implement dug sideways into the plastic just inside the filter to lever it out.
In most services the filter can be cleaned and does not need to be changed, we never replace ours.
If the filter clogs regularly remove it completely and fit a small external fuel filter. Eberspacher say the normal type with a paper filter can have problems with waxing up in cold weather, the Eberspacher version has a metal grid filter element.
One user reported that removing the filter caused air leaks and a small fibre washer was fitted to eliminate this.
The nut at the end closest to the terminals holds a ball bearing and spring non return valve. Do not undo this unless needed as the spring is very easily lost. Also it can alter the fuel rate.

Fuel quantity test.
The fuel quantity test is an important check of the quantity of fuel delivered to the Eberspacher.
Do this test if you suspect a fuel problem.
It checks for blocked fuel filter, blocked or kinked pipes, loose connections, air leaks, faulty pump, or incorrectly installed piping.
If the pump does not deliver sufficient fuel it can cause difficulty starting, flame-outs and white smoke.
Too much fuel can cause overheating, black smoke and the heater to carbon up.
Details of the test are on this page.
Normal air bubbles in fuel pipe are very small and about half an inch apart. It may take several starts to drop to this size. Some are too small to be visible in this photo.  More bubbles indicate a small air leak.
Very large bubbles indicate an air leak or lack of fuel.

Fuel pipes and pickup.
We found that although you can blow through completely empty pipe it becomes impossible to do so with even a small amount of fuel in the pipe. This can cause users to wrongly think the pipe is blocked.
If the pipes are blocked it is normally because the heater has not been used and the fuel has turned to jelly. Skip from Tennessee USA attached a small clear gas line to the hard plastic fuel line, filled it with acetone (alternative solvents like carb cleaner can be used) and let it sit for about an hour. The fumes and fluid would have softened the blockage before he applied low air pressure to force the fluid through the blockage.  Then he flushed the line with diesel.
The rubber connecting sleeves can swell when they deteriorate.
Carbon build up can obstruct the fuel flow where it enters onto the glow-plug screen.

If the heater takes fuel from the main tank a separate fuel pickup pipe is normally used.
The end of the pickup tube is normally cut so it is between 1 and 4 inches short of the tank bottom. This ensures there will be enough fuel left to run the engine and prevents water and crud in the bottom of the tank from being picked up. This can cause users to think the heater is faulty when the heater stops due to lack of fuel as there is still fuel in the tank.
The pipe on some types of pick up tubes is a push fit into the upper part and this can cause air leak problems.
If the pickup pipe is too large the fuel may trickle back.
Blockages can occur in the pipes but are most likely at the pickup, the filter or connecting sleeves.
An air compressor or bicycle pump will clear pipes, we use one to remove the fuel from our temporary testing pipes before storing them.

Drilling a vehicle's plastic tank will void its approval. You may have to replace the cartridge type fitting with one from Eberspacher designed for that vehicle. Plastic swarf created during drilling floats on the fuel surface with obvious consequences.
Fuel pipe from the pump to the Eberspacher D2 is usually hard fairly clear plastic, 4mm outer and 1.5mm or 2mm internal diameter. Maximum height lift for a D2 from the pump to the Eberspacher is 2m. The pipe from the pump to the fuel tank is usually black hard plastic 5mm outer and 2mm internal diameter. Maximum height lift from the bottom of the tank to the pump is 1m.
The proper fuel pipe is difficult to kink or compress. Do not use cheaper soft plastic pipe which can kink badly.
Do not crush the pipe when cutting. A pipe with a burr or sharp end can slice into the rubber as it is inserted forming a flap, photo on the Faults page.
Large diameter fuel pipes can cause several problems including not priming the pipes, non starting and flame-outs. A 1m length of 1.5mm internal diameter pipe is filled by nearly 2ml of fuel. The same length of pipe with 4mm internal diameter would hold 7 times that amount and would take 7 times as many pulses to prime. This is why we always use the correct fuel pipe, ebay lists 2mm internal diameter Eberspacher fuel pipe.
Where pipes are joined they should butt against each other inside the rubber connecting sleeve, gaps can trap air bubbles.
There are restrictions on teeing from the existing engine fuel supply pipes, read the Eberspacher manuals carefully.
There is one statement in some of the Eberspacher installation manuals about gravity feeding that is not fully explained and so could be misunderstood. Gravity feeding to the pump is ok, gravity feeding without a pump is not allowed. Maximum height of fuel above pump is 3m.
Marine installations must use metal pipes and comply with all regulations.

Soft pipe kinks easily blocking the supply.
The rubber connecting pipes can cause air leaks.

If insufficient fuel reaches the Eberspacher the flame will extinguish and the flame-out causes the heater to shut down.
The most common reasons for restricted fuel flow are blocked fuel filter, kinked pipe, air leaks, air lock or running out of fuel.
Water in the fuel collects in the bottom of the tank, as this sloshes about it can be picked up replacing the fuel.
Unsuitable fuel can cause flame-outs at low temperature particularly at the lowest heat setting.
Note flame-outs can also be caused by a clogged glowplug screen, blocked breather hole, heavy carbon deposits as well as blockages in the combustion air flow or exhaust.

Fuel pumping rates.
The pump rate increases together with the fan speed with each heat setting.
Sometimes it may be useful to know at what setting the heater was operating when a fault occurs.
Fan speeds where known are quoted on the Faults page but the fan may not be accessible.
The manuals do not give pump rates so we have no figures for most heaters, details will be added here later if we measure them.
D2  low  80,   med 121,  High 187,   Boost  223    strokes per minute.
D4  low 104,  med 201,  High 306,   Boost  411    strokes per minute.

Older pump from my Eberspacher D1LCC.

Airtronic D2 and D4 pump.

Note 1  Suitable for operation with FAME according DIN EN 14214 in flowing capable condition.
              Fuel thickens when temperature drops below 0°C.
Note 2  Operation of the heater with up to 10% more biodiesel added to the manufactured road diesel without restriction is possible, ie heater can work with about 20% total.
            We think the D1LC compact heater group should also be marked with Note 2, it was missing on the copy we obtained.

These instructions given in the AIRTRONIC D4 manual probably also apply to any of the models capable of using Biodiesel:
Operation of heater with mixtures greater than 10% is restricted during periods of temperatures below 0°C.
Vent hole must be cleaned every 500 hours (twice a heating season assuming 1000 hours of operation annually).
Atomizing Screen must be replaced every 500 hours.
Heater must be run for 30 min on high heat with regular diesel fuel once every 500 hours if mixtures above 50% are used.
When using 100% biodiesel, the heater should be operated twice a year with diesel fuel (in the middle and at the end of a heating period) to burn off PME deposits. Let the vehicle tank run almost empty and fill with diesel fuel without any biodiesel. While running on this tank filling, switch the heater on 2 to 3 times for 30 minutes at a time at the highest temperature setting.
Biodiesel produces about 10% less heat per litre than normal diesel and poor oxidation stability means additives may be needed to improve storage conditions.
Biodiesel is an excellent medium for microbial growth which is accelerated by water so special care must be taken to remove water from fuel storage tanks to avoid sediment buildup, premature filter clogging or storage tank corrosion.
Diesel engines & heaters that are not designed for biodiesel can suffer from filter clogging, coking and rubber seal damage.
Home made or roadside bio fuels are very different to EN 14214 spec oil.

Fuels not recommended for Eberspacher heaters.
Supermarket vegetable oil (New or Used frying oil) unless properly processed into FAME.
Fuels mixed with used oil.
The amount of money saved on these fuels will be insignificant compared to your additional servicing and repair costs.

Heater Model
100% FAME Operation
Note 1
Operation with road diesel which currently contains
10 to 12 % Biodiesel
AIRTRONIC D2 / D2 Camper
25 2069 05 00 00 /
25 2326 05 00 00
Yes     Note 2
25 2113 05 00 00 /
25 2114 05 00 00
Yes     Note 2
25 2144 05 00 00 /
25 2145 05 00 00
Yes     Note 2
25 2361 05 00 00 /
25 2362 05 00 00

Yes     Note 2
AIRTRONIC D3 Camper / D4 Camper /
D4 Camper plus
25 2317 05 00 00 /
25 2318 05 00 00 /
25 2327 05 00 00
Yes     Note 2
All versions
Yes     Note 2
HYDRONIC D 5 W S  24 Volt (!)
25 2146 05 00 00 /
25 2218 05 00 00
Yes     Note 2
All versions
HYDRONIC 16/24/30/35
All versions
Air heaters D1LC compact /
D3LC compact / D3LP compact / D5LC
All versions
probably also Note 2
Air heater D8 L C
All versions
Eberspacher Fuel supply Faults 2.
Performing a Fuel quantity test.
The fuel quantity test is an important check of the quantity of fuel delivered to the Eberspacher.

Fuel volume test method, D1LCC, D3LCC, Airtronic D2 D4 D5, Hydronic 10, DW4SC, DW5SC.
Disconnect the fuel pipe from the Eberspacher fuel inlet and insert it in a small container to catch the pumped fuel. The container can be a graduated 10ml or 20ml cylinder so the result can be read directly, or a bit less high tech, a small aluminum foil pie dish plus a 5ml syringe, no needle, which should be available at any pharmacy for less than £1.
Fuel will exit the pipe during the test in reasonably powerful squirts, if it trickles out it shows there is a problem
Switch the heater on and once pump starts let it run to bleed any air for about a minute, then switch off and empty container.
Switch the heater on, the pump will start after about 60 seconds with a D2 or D4.
Hold the end of the pipe in the container level with the glow pin while fuel is being delivered, between 90 and 110 seconds. We know of instances where it tested ok when held at a lower level despite there being a fuel supply problem.
Once the pump stops switch off the heater and measure the quantity of fuel.    Note cc, ml and cm3 are the same volume.
Fuel quantity in cc (or ml) should be between:  D1LCC  3.4 to 4.65,    D3LCC 7.1 to 9.3,    D2   3.7 to 4.4,    D4   5.0 to 6.4,   D5  8 to 10,     D4WSC   7.3 to 7.9,    D5WSC   8.5 to 9.0,   Hydronic 10   9.1 to 10.2.
The fuel quantity for these models should not be affected by normal voltage variations.
If the fuel volume is low or out of specification check for blocked filter or pipes, air leaks, incorrectly installed pump etc.
High fuel volume is probably caused by incorrect fuel tap off point (see manuals) or wrong pump.

Low fuel volume can cause flame outs.
High fuel volume can cause overheating shutdowns and wasted fuel.
We know one user bought a D1LCC which came with a D2/D4 pump (test result bottom of page)

Alternative test method.
If you are testing on your own and the heater start switch is remote from the heater you can alter the test method slightly for a D2.
Do not switch off after 60 seconds, let it continue until it stops after the first start attempt, empty the fuel into a spare container and use the second start for the fuel measurement. The quantity pumped by the D2 second start will be about 5% lower than on the first attempt as the number of pump strokes is reduced from 189 to 180. The D4 second start attempt  is much shorter than the first
We do not know about other models.
These time measurements taken on our heaters show how long you have between stages.


The easiest way to measure is a measuring cylinder.
10 ml one used here, £1 ebay.
My D1LCC fuel volume test result 4 ml.
Alternatively use a syringe.

Old foil pie dish makes an alternative container.
Tuna can just made the dish easier to handle.
The fuel spurts out under pressure.
Tilt dish before sucking fuel into syringe.

5 ml syringe from local pharmacy.
Don't use it for baby afterwards.

Air bubbles should be removed before measurement. Hold syringe upright and then press plunger very carefully. Too much pressure and fuel squirts out, needing another test.

Some users worry if the test volume is not close to the middle figure, eg with a D2 about 4cc, and think something is wrong. If the volume is near the lower limit it could be worth checking the filter and for any air leaks as a precaution but don't worry. Any pump within the quoted limit should work with any D2 heater so if the pump measures 3.7 cc it passes the test and is ok.
A pump does not simply work ok at 3.7 cc and then fail to work as soon as it drops outside the limit to 3.6 cc.
Outside the limits is an area of uncertainty. Depending upon how far out of spec the pump is, it could work ok with some D2s but not others, it might only work with a heater in good condition, it might work only with some types of fuel etc. It also could increase the rate of carbon buildup needing more frequent servicing.
If the fuel quantity result is below specification Eberspacher recommend that the fuel pump be replaced only if the heater repeatedly flames out during operation.

Older models such as D1L,  D3L, D1LC, D4W and D5W require the glowpin to be disconnected during part of the test and their readings are voltage dependent so are not covered here, look at the manual for detailed instructions and their fuel volume graphs.

If the wrong amount of fuel is delivered and all other causes except the pump have been eliminated check the pump clamp fixing bolt has not loosened allowing the pump to move to horizontal.
It might be possible to adjust the pump, details are in the 'Pump' section above.
Pump Electrical.
Eberspacher use a pulsed type pump. Once power is applied it operates a solenoid which produces a single spurt of fuel.
The power has to be removed so the solenoid can return to its starting position before the next pumping stroke.
The pump power is pulsed on and off to operate, this is done by the Electronic Control Unit (ECU).
The ECU sends pulses of +8v for a 12v D2 or D4 heater on the green/red wire, faster pulses give more fuel, slower less fuel.
The brown wire of the pump is connected to the battery negative supply, the joint is sometimes hidden inside the wiring loom.
The pump is not polarity sensitive so connections can be either way round.
Unlike older heaters the pump on modern models does not start pulsing immediately the heater is switched on, the Eberspacher does some checks and preheats for between 15 and 60 seconds before starting pumping.
Note multimeters are not designed to measure pulsed voltages, readings will be meaningless and can be different for different makes of meter.
A steady non pulsed voltage on the pump will not pump fuel, but it can get hot. In that case check the pump is ok as below. Check for a short circuit on the pump wire to +12v, otherwise replace ECU. If measuring this steady voltage the pump has to be connected otherwise you can get incorrect readings.
The resistance of an Eberspacher D1LCC, D2, D4 or D5 pump should measure 10 ± 0.5 ohms (24v 36 ± 1.8 ohms)
A 24v pump tested on a 12v heater receives 1/4 of the pulse power, it passed the start up checks but did not click or pump.
Check the connections for corrosion and the wires for mechanical damage.
[For the technically inclined only - Pulse measured on oscilloscope about 40ms constant width, variable pulse rate]

Testing the pump with a 12v (or 24v) battery.
WARNING Failure to disconnect the pump wiring before doing this test can damage the ECU.
Connecting the battery to the loom instead of the pump also damages the ECU.
Connect a wire from one pump terminal to the battery.
Connect the second wire from the other pump terminal and dab it on the other battery terminal which will give a single pulse of fuel.
The wire has to be disconnected and reconnected for each pulse.
A small spark is usually visible as this is done together with a loud click from the pump solenoid.
If it does not click the pump may have either an electrical fault, check its resistance as above, or a mechanical fault.
If it clicks but does not deliver fuel see Pump Mechanical section.
Weak clicks may be caused by electrical or mechanical faults. A 24v pump on a 12v heater could also cause this symptom.
After a sticking pump was removed and the fault cleared one user wanted to check if it was working before going fifty miles back to the boat. The number of pulses here are only very rough initial estimates, at best only confirming the pump may work.
D2 roughly 50 pulses per ml, D1LC roughly 60 pulses per ml, D1LCC roughly 65 pulses per ml.
Measured number of pulses per start attempt:  D1LCC  257.
D4L manual quotes 200 strokes for 5.5 to 6.0 ml and 316 to 350 strokes per minute on full.
A fuel volume test will still be needed if the pump has been disassembled.

Pump Mechanical.
Pump problems usually happen if the heater is not used regularly and may be caused by gummy fuel deposits inside the pump.
Eberspacher say regardless of the season, run the heater every month for a minimum period of 15 minutes which will ensure that the fuel in the pump and lines to the heater does not gel and solidify. We run ours only once or twice during summer, we are using kerosene which might gel less.
Pumps use the fuel as the lubricant. Mounting the pump horizontally or below the minimum 15 degree angle can cause air bubbles to be trapped which can either block fuel flow or prevent lubrication to parts of the pump resulting in mechanical damage and pump jamming.
The pump clicks are quite loud and are louder with no fuel than when full of fuel.

If it does not click during bench testing it may have mechanically stuck but read Pump not clicking section at top of page first.
Sometimes it can be freed by banging with a lump of wood.
One reason for not working in cold weather could be fuel waxing or water freezing inside the pump.
If the pump is clicking and the tests at the top of this page do not solve the problem try immersing the bottom fitting completely in the fuel while testing to eliminate the possibility of an air leak in the connector or lower piping.
Faulty pump
Remove the pump and bench test it as described above.
Check the filter in the base of the pump is clean.
Dismantle the pump as shown making sure you don't lose the spring and ball bearing.
   Clean the ball bearing and the bottom of the tube where it makes contact, this is a one way valve so dirt can stop it working.
   Check the spring is clean and looks in good condition. Clean the tube containing the spring.
If the reassembled pump still does not pump try more drastic methods.
Blow through with a bicycle pump or a compressor. Start with low pressure.

Pump Dismantling.
Fully dismantle the pump only if necessary, be extremely careful as the ball bearing and spring which create a one way valve are very easily lost, both during dismantling and handling. Placing the pump in a cardboard box may help catch springs. I found a cereal box ideal. Alternatively undo inside a plastic bag. Even gripping a spring gently by the ends caused it to fly. After searching for it on 3 occasions during testing and photographing I now always grip them gently by the sides.
If the pump is adjustable mark the nut and record its position before undoing, the nut may not be fully tightened.
Ian Whittaker found fully screwing the fitting home on his pump interfered with the free movement of the ball and prevented the pump working. He suggested using an O ring to hold the shoulder away from the body.
When replacing the spring take care to insert it straight, preferably hold pump vertical and allow it to fall onto the ball bearing. When initially replacing mine with the pump at an angle I felt it catch slightly on the side of the bore so re-inserted it. This was almost certainly the cause of one pump spring found with the end bent over so it did not seat properly on the ball bearing.
After reassembly of any disassembled pump you need to do a fuel quantity test to check its calibration.
D1L pump dismantled.

Airtronic D2 / D4 pump dismantled.
The output end of the pump body contains a black seal at the bottom of the outlet which is not shown here.

Alternative pumps.
Be very careful before buying pumps if they do not specify the heater type or voltage.
Do not simply compare the kW ratings of pumps, they can be designed for different pulse rates.
Original pump spring and replacement spring test.
Arrow shows compression distance for 35 gm pressure.

Lost pump spring and ball bearing or small O ring.
Thanks to Mike Coats who was missing the smallest O ring and found an ebay source - Sealforce 01382489043   £1.99 for 10. He measured the O ring slot as 2.71mm and 1.15mm wide so assumes the O ring will be 1mm wide. The bore it fits in is 4mm. Sealforce sent him a selection of different sizes and the 2.7mm fitted best.
If you have dismantled the pump and lost the spring / ball bearing you can buy them on ebay for about £5.
If these are not available and you are tempted to try any old spring / ball the following may help prevent wasted time. In the old Eberspacher D1L pump shown above and in a D2 pump the ball bearings measured 4.44 mm diameter. The springs which were very weak, 10mm long, 3.15 mm diameter and held the ball against the fuel outlet to act as a one way valve. The D1L spring was placed in the outlet pipe and compressed against some kitchen scales until they just about touched the pipe. The contact point was difficult to judge and my best guess was roughly 35 grams.
Stronger springs will reduce or stop the fuel flow as will not having a spring fitted.

Solenoid pumps - How they work.
Eberspacher fuel pumps are sealed so investigation of what is inside would not be easy. If you have a faulty pump please donate it.
Thanks to Andrew Leonard for donating a faulty D2 pump which we hope to cut open for photographs for the page.
There is a good explanation of a solenoid pump at www.kcsaab.com/aquamist/website/cp/sys1/techsys1/pump.html.
There are some obvious differences from Eberspacher versions but this does explain the basic principles of solenoid pumps.

Test Heater Model
Test Heater fuel spec
Pump Model on test
Pumped fuel volume
Test result


Airtronic D2
3.7 to 4.4 ml
Airtronic D2/D4   pump 1
3.7 ml
Airtronic D2
3.7 to 4.4 ml
Airtronic D2/D4   pump 2
4 ml
3.4 to 4.65 ml
D1LCC  pump 1 vertical
4 ml
3.4 to 4.65 ml
D1LCC  pump 1 sloping
approx 3.9 ml


Airtronic D2
3.7 to 4.4 ml
D1LCC  pump 1
3 ml
Too low,  fail
Airtronic D2 (User test)
3.7 to 4.4 ml
Webasto 9012868C
14 ml
Very high, fail
Airtronic D2
3.7 to 4.4 ml
2.6 ml
Too low,  fail
Airtronic D2
3.7 to 4.4 ml
8 ml
Very high, fail
Airtronic D2
3.7 to 4.4 ml
Hydronic 10
9 ml
Very high, fail
3.4 to 4.65 ml
Airtronic D2/D4   pump 2
5.6 ml
Too high, fail
D1LCC (User test**)
3.4 to 4.65 ml
Airtronic D2/D4 (User)
5.3 ml
Too high, fail
Airtronic D2 12v
3.7 to 4.4 ml
Hydronic 10  24v,
(wrong voltage pump test, should be 12v)
no pumping

Fuel volume test results for various heater and pump model combinations.
During manufacture pumps are set to deliver the optimum amount of fuel for a particular heater model.
This means pumps from one model will not be suitable for other models without adjustment.
We have tested alternative pumps on our heaters. No attempt was made to try adjusting pumps before testing.
We would appreciate if anyone is able to provide test results for any other combinations of heater with incorrect pump, (user tests).
The D1LCC user test** was the result of someone who bought a D1LCC on ebay which came supplied with a wrong D2 pump. That resulted in a condition where the Eberspacher overheated and shut down after 4 minutes only when used on the high heat setting with the fuel can in the van. On lower settings or with the fuel can on the ground it ran continuously but presumably would have not have lasted long before it failed.
The heater was just at the point of failure with the pump delivering nearly 15% extra fuel than the allowable maximum.
A second user has confirmed their heater also overheated and shut down with excess fuel.
Three types of Webasto pumps.
They are not interchangeable with Eberspacher pumps.
Fortunately Webasto pumps are differently shaped to Eberspacher pumps so are fairly easy to identify.

The center pump in the picture on the left is a Webasto 9012868C or 1320292A and is advertised as suitable for most Webasto petrol models from 2 to 5 kw so you might think it would work on similar rated Eberspacher diesel heaters, not so.
This one was sold on ebay as suitable for Eberspacher heaters. When it was fitted to an Airtronic D2 it pumped 3 times as much fuel as the correct pump, definitely unsuitable.
Photo Tony McNicholl.

Check if you have run out of or are simply low on fuel, a tank pick up tube can be 50mm or more above the tank bottom. This ensures there will be enough fuel left to run the engine and prevents crud in the bottom of the tank from being picked up. On one camper van the tank held diesel for about 250 miles but the heater stoped working after 200 miles.
If the fuel pipes were empty before starting check if purging of air is complete.
Check the fuel lines and connections for air leaks
Check all clips are tight.
Check condition of rubber sleeves, they swell and can become porous as they deteriorate.
Check for blockages in pipes, more details lower on this page.
In very cold weather any water in the fuel can freeze.
Most UK fuel sold at the pumps is winterised from September onwards, summer fuel will wax up at relatively mild temperatures.
Check the fuel pick-up pipe, on some non Eberspacher types the tube pushes into the upper part and can have an air leak or it might have fallen off.
Check the fuel filter in the base of the pump.

Remove the pump and bench test it as described in Testing with a battery section.
  If pump is faulty look at the Pump Mechanical section.
Pump clicking but no fuel delivered to heater.
People assume that because the pump is not clicking it is faulty and remove it, then most find it is not faulty.
   When the heater is started the ECU makes a number of checks as described on the Faults page.
   If any of these pre-start checks fail the ECU aborts the startup and no fuel is pumped.
  Look at the Faults page first to eliminate those causes.
If the heater passes the pre-start checks and the blower speeds indicate everything is proceeding as it would normally but the pump is not clicking check the electrical connections.
A fairly common problem on Airtronic pumps is not pushing the connector fully home, it has a locking clip and this has to be squeezed in while fitting.
Then go to the Pump Mechanical section below.
Note pumping is delayed on modern heaters for up to a minute after switching on while the glowpin preheats.

Pump not clicking.
Skip in Tennessee USA had success with the compressor. You could also try pulsing it at the same time.
He also found his fuel lines were gummed up and blocked so he attached a small clear gas line to the hard plastic fuel line, filled it with acetone (alternative possibly carb cleaner) and let it sit for about an hour. The fumes and fluid would have softened the blockage before he applied low air pressure to force the fluid through the blockage.  It worked then he flushed the line with diesel. This method could also be used with a blocked pump.
Another solution I have seen mentioned on forums is drastic but if the pump is crackered you have little to lose, however we have not tried it ourselves so it's your decision.
Remove the fuel filter which is located in the pump body and the rubber connecting pipes before heating the pump in an oven at 200 degrees C, gas mark 6, for about 10 minutes. Test it again without fuel while it is still hot, try banging it at the same time if it is not clicking.
Any alternative suggestions are welcome.

Please give us feedback on these and other solutions, we learn from feedback.

Douglas Greer had the same problem with his Webasto pump clicking but not pumping. He says Webasto fuel pumps cannot be taken apart. Using a bicycle pump solved the problem and saved him from buying a new one. Nice to see our Eberspacher pages even help Webasto owners!

Heater Model
Switch on
Pump start try 1
Pump stop try 1
Pump start try 2
Pump stop try 2
Fan stop

Airtronic D2
Airtronic D4
Airtronic type fuel connector.
Metal spring in locked position, Left.
Push in & release position, Right.

If connector is fitted without depressing spring it is prevented from pushing fully home and does not make a connection, a fairly common fault.