Le Tonkinois Varnish

B & D Murkin

UK main importers for

Le Tonkinois varnish

Flexidisc sander


rpmmeasure1_big.jpg rpmmeasure2_big.jpg

Non contact RPM meter from Ebay.

Kit contains a length of adhesive reflective strip for Eberspacher models which do not have a white stripe.

Does not work in bright sunlight but is ok with overcast daylight.

Point the laser from the side onto the white stripe on the air intake impeller to get a measurement of rotation rate.

Melted hose caused by a break in the inner core allowing hot air into contact with the plastic outer covering.

The inner hose fell apart during removal.

blowermotorclearance_big.jpg

Checking the blower motor combustion impeller clearance with a 0.3 mm feeler gauge. The gap is the same on all Eberspacher heaters except Hydronic 16-35 kw models.

Complete diagnosis and repair Part 2

Faults during running


The Eberspacher ignites normally, drops back and switches off into stand-by mode, blower is slowly spinning but the heater never restarts.   No fault code.

The heater thinks the air temperature is higher than the temperature control setting. Is the temperature control set too low? If not temporarily replace the temperature control with a 2200 ohm resistor as described in Stage 2, this simulates a high heat setting. If the control is not faulty the temperature sensor in the ECU might have failed. In practice this is not something we have encountered and it is impossible to diagnose without installing an external temperature sensor.

Note the blower motor on Airtronic heaters fitted with a remote sensor will be stationary in stand-by mode, not slowly spinning. I do not know if it is the same on any other models.

If a remote sensor is already fitted is it receiving heat from somewhere, like hot pipes behind the panel or something hot below it?

This is also an ECU failure symptom.


Eberspacher starts normally but stops whilst running, it may try to restart.     Fault codes 053, 054, 055, 056

The Eberspacher has flamed out. If the air / fuel mixture proportions change too much the flame will extinguish and the flame-out causes the heater to shut down.

If a flame out happens after the heater has started, the heater will attempt one restart. If another flame out occurs within 10 minutes the heater will not restart.

The most common reasons are no fuel, bad pipe connections, blocked fuel filter, blocked or kinked pipe, air leaks or an air lock.

Rubber connectors deteriorate. They swell constricting the flow, often become porous, bits and flaps of rubber can cause blockages. They can also fail to reseal after disconnection. They should be renewed periodically.

fuelpipe01_big.jpg

This flap partially blocked the rubber fuel pipe.

Flaps are usually caused by inserting a pipe with a sharp edge.


Photo Matt Dimmick


Water in the fuel collects at the bottom of the tank and too much obviously prevents combustion. Smaller amounts sloshing about can be picked up and cause intermittent flame failure.

Wrong pump or the pump at an angle of less than 15 degrees can deliver the wrong amount of fuel. (more info on fuel page)

Unsuitable or degraded fuel can cause flame-outs at low temperature particularly at the lowest heat setting.

Flame-outs may be caused by a clogged glowpin screen, blocked breather hole, blockages inside the burner, heavy carbon deposits as well as blockages in the combustion air flow or exhaust system including the silencer. Cleaning a burner mechanically during a service will not remove deposits inside the inaccessible parts, a chemical clean may be required.

Also check the Start failure category as causes can be the same.

More causes and details in the fuel and servicing pages.

If a flame out happens after the heater has started, the heater will attempt one restart.

If another flame outs occurs within 10 minutes the heater will not restart.

Low battery voltage can also stop the heater, full details are on the low voltage page.


The following are not common but if all the above have been eliminated they may be worth investigating:

The combustion impeller to blower body gap is 0.3 mm and is critical for how much air is pumped.

Check using a feeler gauge at several points in case the fan is distorted or bent.

The combustion impeller is pressed onto the splined shaft on D2 & D4 models so can be adjusted.

The fuel pump may be intermittent. One pump had dirt on the ball bearing valve seat, it passed a fuel quantity test ok.

Burners have a finite life and can eventually fail. Unlikely to develop suddenly, usually will develop slowly over several months / years. There is no easy way of diagnosing burner failure, eliminate all other causes first. Then usually eliminate by substituting a known good burner.

Heater starts normally but stops whilst running. It does not try to restart.   Fault codes 012, 015, 017

The Eberspacher has overheated.

Overheat shut down can occur if there is a restriction of either the heating or the combustion air flows.

Often it is caused by bags or luggage blocking hot air outlets, results can be minor or extremely expensive.

If the blockage is minor (Fault code 12) it can be reset by switching off and then back on again.

More serious blockages or repeated faults can cause the ECU to lock up. (Fault codes 015, 017). The ECU can be unlocked with appropriate equipment. Complete blockages can cause the ECU to be damaged.

Overheats are potentially dangerous and can damage the ECU so don't just keep resetting without finding the cause.

Tip: Check to see if the heated air outlet(s) could be accidentally blocked. If you cannot guarantee they will always be clear fit a protective cage or split the duct to feed multiple outlets so one is always clear.

Check for an obstructed heating air inlet or outlet or for crushed / melted air ducting hose (pictures below).

Check combustion air inlet, it draws air from the exterior and can sometimes be blocked by rubbish such as pieces of plastic debris.

Air inlet silencers may contain foam which can deteriorate and cause blockages, see Buying pages for details.

Check for blockages of exhaust pipes and silencer, carbon build up or exhaust sealant are common causes.

Is the heating air inlet clogged with fluff?  Are all, or to many, heating outlets adjusted to the no or low airflow condition?

Measure resistance of both the overheat sensor and flame sensor as detailed in the Stage 2 tests.

Check the overheat and flame sensor plugs and sockets for dirt or corrosion.

Check motor speed.

Is the Eberspacher clogged with carbon and in need of a service?, servicing details are on our service pages.

Is the pumped fuel volume too high?, do a fuel quantity test as detailed in the fuel page.

If you have altered the heating air ducting check length / number of fittings etc is within specification.

Do the duct compliance test on page 2 of our ducting pages.

Note changing from a straight outlet  to a right angled hood can reduce the ducting allowance by up to 50%.

Poor ventilation around the heater is another possibility.

The overheat sensor is clamped to the outside of the heat exchanger casing at the top of the heater. Various temperatures have been mentioned, we have heard it triggers at about 120 deg C for a D2 and 150 deg C for a D4 but cannot be sure. The actual setting is determined by the ECU software and can vary under specific conditions. The sensor returns to normal when the heater cools down.

Blocked outlets have damaged several of our readers ECUs, see above to prevent this. We know of one Eberspacher where changes to the ducting damaged the ECU and melted the plastic combustion air impeller.

Another user crushed the case which jammed the impeller and the overheat damaged his sensor, photos on the autopsy page.

Some heaters will be locked out if there are too many overheat faults, cure fault before resetting with appropriate equipment.


Airtronic D2 D4 and D5 heaters will lock out in extreme overheat conditions.

This is my best guess as to why the overheat sensor sometimes fails to stop this happening.

If the heating airflow is partially blocked there will still be some transfer of heat to the airflow, temperatures inside the heat exchanger will build up relatively slowly and the overheat sensor will shut off the heater with fault code 12, the fan will then continue running allowing some cooling after fuel is stopped.

However if the heating airflow is almost completely blocked there will be very little heat transferred by the airflow. It takes time for the heat to transfer through the casing of the heat exchanger and the base of the overheat sensor so there will be a delay in detecting the overheating. Once the sensor does reach the normal overheat temperature limit the ECU shuts down the heater. During that delay the heater continues burning fuel and much more heat is transferred to the heat exchanger inner surfaces.  That heat then flows through the heat exchanger to the outside of the casing and without sufficient cooling airflow the temperature rises rapidly until the overheat sensor is too hot for the system to measure. At that point the ECU is locked as a safety precaution to prevent the heater being restarted. A diagnostic readout would then give three fault codes, 12 Overheat, followed by 17 and 15  Excessive overheating.

If there is no airflow the heat exchanger outside temperature can continue to climb above the lock out limit.

While all this is happening some of the heat transfers to the ECU and if its temperature becomes too high components inside can fail.

Once the heater has cooled down the ECU can be unlocked provided it is not damaged

Another reason for these codes could be an intermittent fault on the overheat sensor.

A D1LCC will lock out the ECU after 3 successive overheat faults

Lockouts can be reset with diagnostic equipment like 701 or 801 controllers.

Eberspacher carbons up regularly requiring frequent servicing or smokes during normal running.

In general Eberspachers like to be worked hard. Prolonged running on the low heat setting with some fuels can cause carbon build up. This can be reduced by regularly running the heater at maximum heat output for about half an hour.

Another reason is the choice of fuel; bio diesel and gas oil carbon up the heater far quicker than white diesel or kerosene.

Derek's D2 was smoking and ready for a service when he changed to 28 second Domestic heating oil (standard kerosene). The smoking cleared and it has run for about 5000 hours mostly on low without any sign of needing a service. He thoroughly recommends this fuel.

Check the fuel pump is not less than 15 degrees from horizontal.

Perform a fuel quantity check, it only needs to be slightly outside limits to affect the burn.

Fuel pumps are set for specific heater models, this test will also show up incorrect pump type.

Check for blockages in the combustion air and exhaust pipes / silencer which obstruct the gas flow.

On boats check fenders are not blocking combustion air or exhaust.

Check the combustion air and exhaust pipes are between 0.2 and 2m long, they do not have to be the same length on a D2 or D4.

Check exhaust gasses are not entering the combustion air inlet.

The maximum combustion air temperature is 25 degrees C, this can be exceeded in some engine compartments, draw air from outside.

Check motor speed. Check gap between combustion air blower and body is 0.3mm with a feeler gauge, this is same for all heaters.

Check for degraded fuel.

If the glowpin screen has not been replaced during the service it may be clogged.

Bigger is usually not better, fitting an oversized heater is not good, it will run on lowest setting or standby most of the time.

Water heaters can suffer badly from carboning up and Eberspacher did investigations and found several reasons and solutions which are covered in Eberspacher Technical Bulletin 281.  It also applies to other boat installations


The heater set temperature control seems to have very little relationship to the ambient temperature.

The set temperature controller usually does not have a temperature sensor inside, all it does is to ask the Eberspacher to set its output for the temperature set on the controller. The heat sensor is located inside the Eberspacher in the inlet for the heated air. This arrangement works ok in a small vehicle cab but is not very good when the Eberspacher is situated far from from the heated area.

It fails completely when the heater is fed from fresh air. The sensor then thinks that the temperature of the outside air is the ambient temperature and of course that does not change as the heated area warms up. Even worse if the outside temperature drops below about + 10°C the heater automatically switches to maximum heat output, completely ignoring the temperature controller setting.

The solution can be to fit a remote temperature sensor. For details and how to get a sensor cheap see the sensor page. The 801 controller has a remote sensor inside but it may still be worth fitting a separate sensor so it can be positioned in a different position to the controller.

See also the next categories.


The heater stays in full power mode.

Is it just too cold? Derek's heaters will not drop to low power if the temperature of the returned air is fairly low even with the controller set to minimum.

See the previous category for heaters drawing fresh air from outside.

If a remote sensor is already fitted it may have failed or its connecting wiring (grey and brown/white wires) may be broken or have bad connections.

Controller faulty.

ECU faulty, we know of at least 2 with this failure symptom.


The heater drops down to low heat prematurely.

If a remote sensor is fitted has something that generates heat been placed below it or near it.

Another likely cause is the returned air being drawn from close to the Eberspacher, ie no inlet air ducting.

The air surrounding the Eberspacher can get hot from the heat passing through the case and the heated air ducting. If the heater is in a space that is not well ventilated that air temperature can easily be 30 degrees C or higher. The manual quotes a maximum allowable air inlet temperature of 40 degrees c. When that air is drawn into the heater the temperature sensor inside the air inlet senses the heat and turns down the heating.

Add a returned air duct and / or improve ventilation around the Eberspacher.

A remote sensor may help.

Check length / number of bends etc of heating ducting is within specification as in the 'Eberspacher starts normally but stops whilst running. It does not try to restart' section. Derek experienced a problem of reducing heat on his D4 which was hooked up to some existing ducting with too many bends.

Check controller.


When the heater switches into standby there is a large temperature drop before it will restart.

This is normal. Eberspacher temperature regulation is not brilliant. They have 4 (less for some models) heat output settings and some tweaking of the control is often required.

According to Eberspacher, Airtronic heaters will maintain a temperature within approximately 4°C (7°F) of the desired heat comfort level by regulating between Power, High, Medium or Low heat output. Should the temperature rise above the desired heat comfort level by 2°C or more, it will then switch off into standby until the air temperature drops down by approximately 4°C. Assuming the 4°C quoted is from the switch off and not from the comfort level temperature the temperature can change by 4°C from when the heater switches off to when the heater is restarted. I am more familiar with temperatures in Fahrenheit, if it switches off at 70°F it might be 63°F before it restarts, distinctly chilly!

This poor temperature control will not be changed by fitting a remote sensor or an alternative controller.

Derek's tip for his Airtronic D2: If you feel cold when heater is in standby just tweak the control higher for a couple of seconds then return it to original setting, that usually restarts it.

Duncan Grey has suggested another way to deduce the difference.

He positioned his remote sensor closer to the heater output so it received some direct heat, making it hotter than the general air temperature. When the heater goes into standby it cools down faster. The temperature setting on the controller has to be set higher but net result is less temperature difference.

Downside of reducing the hysteresis is shorter running time per cycle and more starts. This probably will increase the need for servicing and make more noise as starts are noisier than normal running.

My own alternative suggestion is to fit a Y piece with an adjustable flap, available on Ebay, one side for heating output, the other diverting some of the heat outside. That way the heating supplied to the cabin can be reduced to a level that keeps the heater running continuously on low setting so it does not switch off. Sounds wasteful but a D2 only uses 0.1L of fuel per hour on lowest setting and you should get a reasonably constant temperature.

I have produced an experimental automatic temperature controlled addon to this Y piece using a servo and the inexpensive Arduino computer. Details on building it will be added later to the site, email me if you need one sooner.


The blower motor speed is monitored continuously during operation.

Shut down will occur if the blower does not start or its speed varies from specification by more then 10% for longer than 30 seconds. If available use a non contact RPM meter to measure speed of blower, otherwise check for obviously wrong speeds.

I bought a non contact laser tachometer / rpm meter on Ebay for £8 including post December 2012.

Quoted speeds are from the manuals but treat these with caution as Eberspacher may change the speeds in later production runs.

  D2  Power 4800 ±140 rpm, Fast 4000 ±120 rpm, Medium 2800 ±80 rpm, Slow 2000 ±60 rpm

  D4  Power 4400 ±130 rpm, Fast 3500 ±100 rpm, Medium 2600 ±80 rpm, Slow 1600 ±50 rpm, Standby measured about 600 rpm.

  D5  Speeds not quoted in manual

  D1LCC  Power  5000 rpm, Fast 4400 rpm,  Medium 3000 rpm   Slow 3000 rpm

  D3LCC  Power  4200 rpm, Fast 4200 rpm,  Medium 2200 rpm   Slow 3000 rpm  (Medium speed is very odd, I suspect an error in the manual)

If RPM is too high, Airtronic, check magnet in impeller, photo Airtronic service page 2. The magnet detector is in the ECU.

If RPM is too low, check for air restrictions or blockage. Check fan is not catching on case or ECU.

Wiring from the ECU to the combined sensor sometimes prevents ECU locating far enough away from fan during fitting, move wires and refit ECU.

Check wiring for short circuit.

Worn bearings and brushes are generally the main reason for motor failures. See blower page for repairs.

Do not connect the motor to 12v battery to test.

If the blower speed is erratic see also the Weird faults section.

More faults are listed in the fault code table in the manual, these two can also be checked out.

Diagnostic cable short circuit.    Fault code 025 new generation ECU only.

The blue / white wire in the loom is only used for diagnostics, check it is not shorting out.

External temp sensor short circuit.    Fault code 061.

The Eberspacher normally uses its internal temperature sensor unless it detects an external sensor.

Disconnect the external sensor and it will be ignored at the next restart.


There are fumes or a mist from the heater when in use, especially just after switch on.

There is often a slight smell during startup especially if the heater does not fire immediately.

This is normal but if it persists do not ignore these problems, there are safety issues.

Unburnt diesel may leak onto the lagging. Check fuel pipes especially clips and rubber sleeve connectors which can become porous.

Often the cause of fumes is a loose exhaust joint or a fracture in the pipe. Exhausts are often lagged, concealing the leak.

Vehicle type silencers are not gas tight and must not be mounted in enclosed spaces, silencer page.

The burner gasket may have failed allowing exhaust gasses into the heating air.

[Eberspacher exhaust gasses are not pleasant and should always be avoided but should not be lethal, there have been no recorded deaths caused by them. Carbon dioxide levels are generally 9-12%. Carbon monoxide is normally about 39 ppm but can vary from 10 ppm to 150 ppm, levels between 100 and 200 ppm can cause a headache.]


The Eberspacher heater runs normally for 1 hour then switches off, it cannot be restarted for another hour.  No fault code.

This is usually an ex BT heater, these were restricted to 1 hour maximum heating time.

Our D1LCC had a 1 hour timer in a black box plugged into a 3 pin connector on the loom. Remove the timer unit and connect the purple wire from the rheostat to the yellow wire on the 3 pin plug to bypass. A photo of the loom modification is on the Eberspacher wiring page.

BT D2s were fitted with a 701 timer with a 1 hour maximum, no continuous operation and no diagnostics. See the controllers page for a partial workaround for the 701.

801 controllers with a I hour limit were available, later generation 801s have this as a selectable option.

More details on the controllers page.


The Eberspacher heater runs ok on slow setting but fails on high.

A second hand D1LCC bought on Ebay overheated and shut down after about 5 minutes whenever it switched to high setting. A pumped fuel volume test showed pump was giving too much fuel, the buyer then identified heater had been sold with a D2 pump.

(http://users.aber.ac.uk/nns/eberspacher/eberspacher%20tale%20of%20woe.html gives the full story)

Fuel feed may be restricted so insufficient fuel reaches the heater.


The Eberspacher heat output is lower than it used to be.

ie the heater has been working fine but now with no changes to the installation it does not produce enough heat.

a) heat output is ok if controller setting is increased. See also The heater drops down to low heat prematurely section. Heater thinks temperature has reached required temperature. If a remote sensor is fitted has anything generating heat been placed below it. Check the obvious, blocked or damaged air ducts, inlets / outlets closed or obstructed, windows left open, temperature set too low.

 b) low maximum heat output.

     Check the items in part a. Give the heater a full service, don't forget to clean the vent hole and to replace the glowpin screen. Low heat output with no or low levels of smoke leads to suspicions of low fuel quantity. Do a fuel quantity test. Check fuel lines for air leaks, blockages, kinks or compression. Check fuel filter in the pump. Check the rubber connecting pipes, when they deteriorate they can become porous or swell. Air bubbles trapped where joints do not butt together and pieces or flaps of rubber shaved by sharp tubing can cause unseen obstructions. Fuel may have partially solidified in very cold conditions. Small droplets of water may have frozen in the pipes. Check the pump has not moved into a horizontal position because of loose fixings or being knocked.

Unburnt fuel will usually produce smoke instead of heat and may smell, restrictions of combustion air or exhaust could be the cause. Fuel may have deteriorated or may simply just be non winterised or unsuitable, see fuel pages. Check the heater is reaching boost or high settings. (Fan and pump speeds will confirm)

If all these are not the solution think about what is happening to get clues as to where to look next.

If combustion air and fuel are properly mixed in the right proportions and burnt then heat is produced which has to go somewhere. If it does not come out of the blown air outlets it must either be raising the heater temperature which would cause overheat shutdown or it is escaping from the ducts. A severe buildup of carbon can insulate the heat exchanger from the burning gases so much of the heat remains and is lost through the exhaust. In extreme cases the exhaust can glow.If these are not the causes the heater is presumably not generating that amount of heat.

Burner may be damaged.


Unit fails after battery is connected or disconnected with controller switch on  -  Fault code 09

This fault code can often be caused by connecting the battery when the Eberspacher controller switch is on. Sometimes it can be reset with appropriate equipment but not always.


Burner problems

Usual symptoms are black smoke and flame outs as the heater ramps up.

Burners have a finite life and the mesh inside can eventually wear out. This is not a normal fault and should generally be considered as very unlikely.  Recently we bought a used D4 burner cheaply from Ebay and cut it in half. Now we can see why they fail and why burners cannot be cleaned by a simple mechanical clean, details and photos.

We had one Eberspacher heater that we helped diagnose. The unit ran ok but would intermittently flame out, sometimes completely but usually only for a second or so before re-igniting. The fault would occasionally not occur for 30 minutes but mostly happened within 5 minutes or less, sometimes about a minute apart. It sounded rougher than usual but had no flame outs. It also sounded unstable with the noise changing over a few seconds. I did at least 20 tests, starting from cold, warm and hot with two types of fuel but could not get any flameouts. The next day was cooler than the previous hot summer day, and I did a few more tests. It flamed out completely on the first test and shut down, when it restarted I could hear short blips as it flamed out and re-ignited. We were then able to swap components with our spare D2 and it turned out to be the burner. The burner looked perfectly clean but we cleaned it ourselves in a chemical cleaning solution. That gave no improvement. The heater was just on the edge of its failure point which is why we had difficulty getting it to fail on the first day.


Weird or intermittent faults

Sometimes the heater has faults that are confusing and don't seem to fit the normal categories.

These type of faults are not usually caused by ECU or component failure.

My first suspicion is usually power feed, either the battery or the battery supply wires both positive and negative and their connections. Flat batteries and low voltage are probably the major cause but are straightforward to diagnose and cure, full details low voltage page. Leisure batteries deteriorate over time often without giving any warning signs, eliminate by substituting a known good battery.

Check for loose or corroded connections in all wiring not just the battery feed and return.

Check the brown/white earth wire, it can cause problems including erratic fan speed or odd controller behaviour. Using the brown earth wire instead of the brown/white can also cause this.

Some battery chargers can cause problems, Ctek chargers connected with cables that are too thin are under suspicion. Voltage spikes on the battery supply can be caused by other equipment, possibly high power devices switching on or off.

Fuel problems like bad fuel or air leaks, fuel pages, can cause the heater to intermittently fail.

Occasionally a service can clear these faults. This may be due to clearing bad connections during the procedure but in one case connections had been unplugged several times and before the service the heater still generated invalid fault codes greater than 100. The heater symptoms also included smoking and failures to start. The only reason I can think that the service solved the problem would be if the ECU itself was overheating. The blown air cools the ECU and it is possible a combination of coked heat exchanger, and too long outlet pipes caused this without tripping the overheat sensors on the heat exchanger. This is purely guesswork, it may or may not be true.


ECU / ICU fault.

The ECU ( Electronic Control Unit) controls all actions of the heater. In later models the name is changed to ICU (Integrated Control Unit). I refer to both of them as ECU on this website, rather than saying ECU / ICU. They are often described as the brains of the heater. ECU failures could cause the majority of the faults listed to occur so I usually do not mention it specifically in the diagnosis. There is no easy way to determine if the ECU is faulty except by fitting it into a working heater or replacing it with a known good one.

Most of the ECU must be working to send the diagnostic information to the controller.

Diagnostic readouts can sometimes mislead as a damaged ECU can indicate components outside the ECU.

I have only heard of one successfully repaired Airtronic ECU. They are also filled with a black material, if anyone can help me find a UK source of chemicals to remove potting compounds I would be very grateful.

Older model ECUs have been repaired but for later models replacing is the only current option.

We learn a lot from faulty components so if you replace one please donate your old one to us.

ECUs are extremely expensive, Ebay may be the cheapest source.


Why do ECUs fail?

Reasons for ECU failures are given on the ECU page.

Eberspacher say they are getting a higher ECU failure rate with heaters fitted on boats than on vehicles.

Factors external to the heater must be the cause otherwise vehicle heaters would suffer the same failures.


Corroded or broken exhaust ports

A small number of heaters suffer from corroded or broken ports. Galvanic corrosion can occur between the alloy port and the stainless steel pipe which can rot the alloy and make the disconnection of the pipe very difficult. This can result in a badly damaged  port and could require a new heat exchanger.

I am currently investigating a couple of repair methods, I have the tools and pipe ready for trying, details will be added when I have time to experiment.

Contact me if you require these details.



General information



Airtronic D4 Normal start up sequence


How the Eberspacher D4 heater should start if there is no fault and everything is working properly.

Stage 1 Switch on.

  When the Airtronic D4 heater is switched on, the indicator light in the control element illuminates showing the heater is on.

Stage 2 Pre start checks.

  The fan runs at medium speed, then drops to slow speed.

  Control unit does an electrical check of the glow pin, flame sensor, temperature sensor, fuel metering pump and control unit.

Stage 3 Preheat.

  Glow pin is energized at 5 seconds point and starts preheating the combustion chamber.

  Fan turns slowly.

Stage 4 Fuel on.

  At 60 second point pump starts at slow rate rate,  At 80 second point fan increases speed gradually.

  White smoke which is unburnt fuel may come from exhaust.  Ignition will take place as the fuel air mixture contacts the glow pin.

  When heater "catches" smoke stops and you hear a jet like noise which increases.

  Once the flame detector detects the flame, in the manual this is shown occurring at the 110 seconds point which is possibly typical, the glow pin is switched off after 80 seconds (190 seconds point in the example).

  After the glow pin is switched off fan speed increases to power setting until burner case reaches target temperature.

     However if the heater does not ignite within 90 seconds after starting the fuel pump the start is repeated.

     If the heater still does not ignite after another 90 seconds of pumping fuel, the heater is switched off,

     i.e. the fuel supply is off and the fan runs on for about 4 minutes.

  The heater is in the “POWER” stage with maximum fan speed, pump speed, fuel quantity and roaring noise.

  Once the heat exchanger reaches optimum temperature the Eberspacher switches into control mode, the pump rate and fan speed are controlled by the ECU to give the required heat output - Boost, High, Medium, Low or Standby.


When the Airtronic D4 is switched off, the fuel pump stops and the glow pin is switched on for 30 seconds to clean off any combustion residues. The fan speed gradually reduces, it continues to run for 4 minutes to cool the heater.

If the heater is restarted and the heat exchanger is too hot the fan will run to cool it before restarting.




Eberspacher D1LCC Normal start up sequence


How the Eberspacher D1LCC heater should start if there is no fault and everything is working properly.

The manuals do not contain much detailed information on the start sequence.

Stage 1 Switch on.

   When the D1LCC heater is switched on, the indicator light in the control element illuminates showing the heater is on.

Stage 2 Pre start checks.

   Control unit does an electrical check, no details given of what components are checked, probably similar to D2.

Stage 3 Preheat.

   Glow pin is energized at 3 seconds point and starts preheating the combustion chamber.

   Fan starts at slow speed.

Stage 4 Fuel on.

   At 15 second point pump starts.

   White smoke which is unburnt fuel may come from exhaust.  Ignition will take place as the fuel air mixture contacts the glow pin.

   When heater "catches" smoke stops and you hear a jet like noise which increases.

   Once the flame detector detects the flame, the glow pin is switched off before 90 second point.

   No information given on when fan speed increases.

      However if the heater does not ignite within 90 seconds after starting the fuel pump the start is repeated.

      If the heater still does not ignite after another 90 seconds of pumping fuel, the heater is switched off,

      i.e. the fuel supply is off and the fan runs on for about 4 minutes.

   The heater is in the “POWER” stage with maximum fan speed, pump speed, fuel quantity and roaring noise.

Once the heat exchanger reaches optimum temperature the Eberspacher switches into control mode, the pump rate and fan speed are controlled by the ECU to give the required heat output - High, Medium, Low or Standby.


When the D1LCC heater is switched off, the fuel pump stops and the glow pin is switched on for 15 seconds to clean off any combustion residues. The fan speed gradually reduces, it continues to run for 3 minutes to cool the heater.

If the heater is restarted and the heat exchanger is too hot the fan will run to cool it before restarting.


Eberspacher Faults 1 Fault codes Fuel faults Voltage Components Servicing Site guide
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Eberspacher heater lockouts


The D1LC and some early D1LC Compact heaters produced between 1990-1998 lock out after 5 unsuccessful physical start attempts (each attempt means two automatic starts to give the 10 starts before lock out). One user confirmed the D5L has the same lockouts.

If the heater starts during these attempts it cancels previous non start fault codes and five new attempts are now available. However should the heater lock out after these five unsuccessful physical start attempts then you will need to get it unlocked. It can also lock out after 3 successive overheat faults.

I don't know how common these lock outs are but most people will try several times to start the heater when they have a problem. We have several reports from users who had no lockouts despite doing many start attempts so would have expected problems. In fact we have only met one locked out heater (D5L) which leads us to suspect it may not be as much a problem as expected.

A locked heater usually has to be unlocked by an Eberspacher dealer or with a diagnostics tool / controller.

It seems to be very poor engineering design by Eberspacher to not provide a way of resetting without special tools.




Eberspacher Airtronic D2 D4 D5 lockouts


Airtonic heaters will lock out after 255 identical minor faults. Any different fault before lockout occurs will reset the counter. Major faults, usually overheating, will lock the heater, possibly after 10 faults but exact details are not published.

'Overheat with excessive temperature' fault conditions will lock the ECU immediately.

Providing no other components are damaged the ECU can be reset with equipment like the diagnostic unit, 7 day timer, 701, 801 or EasyStart Select controllers.


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This port is not good for getting a gas tight seal.

D1L exhaust port rotted away.

We hope to repair it as a trial.

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