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Flexidisc sander

Eberspacher Airtronic D2 & D4 service 2

Examining the parts & locating the problem

Previous overhauls of some earlier Eberspacher D1LC compact versions had us up to our knees in crud.

With this D2 it was a case of do I need to wash my hands. The bottom end of the glow pin was spotless - as good as new!  After at least 2000 hours, not a trace of carbon. The burner combustion tube was exactly the same - a finger rubbed around both outer and inner surface came out clean!

The heat exchanger fins were coated in a thin film of loose powdered soot. A quick rub with a toothbrush brought them up as clean as new. Same applied to the exhaust port and pipe.

The glow pin screen was less clean, it had a small buildup of carbon between the mesh and was causing the starting problems. Parts shown are exactly as they came out - no manual cleaning beforehand, apart from the final two of the heat exchanger. Compare these photos with an extremely bad D1LC Compact shown on the D1LCC service pages

Click on images for better quality.

Eberspacher D2 parts, no additional cleaning

Heat exchanger channels before brushing. The scratches on the top were made checking the deposit thickness.

An old type screen removed intact and new type screen taken apart, showing the screen has 5 mesh layers.

We advise always to replace the screen as residues can be trapped between the multiple layers and not be visible. The screen disperses the fuel aiding the atomising process. It is also coated with a catalyst to assist combustion.

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Clogged screen which caused the flame out problem.

This screen had a slot for the breather hole.

Crumpling was done during removal.

New replacement screens are shorter with no slot. They will fit all D2 & D4 heaters and come with an insertion tool. Eberspacher recommend annual replacement.


Bottom of the heat exchanger channels before brushing.

Eberspacher D2 heater reassembly

Reassembling the unit is the reverse of the disassembly process with just a couple of points to note.

Some users recommend using Copaslip on bolts, not essential but it might help future servicing.

The resulting debris.


Modern fuels are a lot cleaner than the notorious old ‘Red Diesel’, actually High Sulphur Gas Oil, sold before 2011 so you are unlikely to meet heaters with as much hard deposits as this very bad D1LC compact we overhauled a couple of weeks previous to the D2.

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Brushing loose debris from the heat exchanger with a toothbrush. No need in this case to use any other cleaning method. It did the job in less than a minute.

The results

The service cured the flame-outs and the Eberspacher Airtronic D2 started reliably every time.

It ran more efficiently and sounded smoother.

I wanted to take a photo of the smoke at startup to show how much smoke it produced.

However after the service there was not enough smoke to see so no good trying to photograph it!

A spare Airtronic D2 of ours that had not been serviced smoked for about 4 seconds on start up

Updates and later problems

After about two months there were a couple more flame-outs.

The small amount of remaining red diesel in the 5L can contained a lot of floating debris.

Derek could have shortened the pick-up pipe so it picked up fuel well clear of the bottom but preferred to top up less frequently. Refilling the can with fresh diesel solved the problem. Later he replaced the can with a 30L tank.

Then in late 2011 he hit problems with fuel degradation which very quickly clogged his main D2.

It was almost a year since the previous service and its annual service was due so he replaced it with his spare D2. The replacement clogged up within 2 days. He stored the diesel in 25L containers and filled the 5L can from them, they had a lot of crud at the bottom. Further investigations revealed fuel degradation was the cause for both of the above problems. Details of the diagnosis are on the Fuel problem page.

More information on this problem is in Eberspacher Technical Bulletin 281.

In Jan 2014 the blower motor noise was getting worse quite quickly and it started to have problems coming out of standby. Fault codes indicated two blower speed errors and one previous blower motor open circuit fault. Considering how many hours it had run since it was bought second hand it was not unexpected.

The motor was clean, no evidence of burner fume deposits, it was a brushes problem. The motor from our spare D2 was changed onto the main D2. Normally he would have done a service at the same time. There was no evidence of crud in the exhaust port and the heater was still running so well that he decided to leave it alone to see how many hours it would keep running on kerosene without a service.

Brushes / bearings problems may not be terminal, we later found out how to disassemble it, see the blower page for details of repairs.

Conclusions and comments

Modern Eberspacher heaters really do need cleaning out regularly - carbon build-up will cause problems.

It can restrict fuel and exhaust flow; reduce the transfer of heat to the warm air duct; cause the unit to overheat. From experience Derek suspected that this combination contributes considerably to ECU failure. A new one costs from around £280. Enough said!.

Update Oct 2013

We have changed fuel from red diesel to Kerosene (domestic grade 28 second heating oil). Kerosene burns so much cleaner that we have not had to service our heaters, even one that was smoking and giving indications of needing a service cleaned itself and has run perfectly since then and looks as if it will continue for many more hours. Derek estimated just before his death it had run for a conservative 8000 hours without requiring a service*, much of that time on low heat setting. (Estimate based on total fuel consumption, average of 8 hours per litre and 75% hours on low setting. Note these figures apply to his particular usage pattern and should not be used as a typical guide  Your average fuel consumption per hour will almost certainly be different.)

* He did have to replace the blower motor due to brushes wearing out during this time.

Finally the reason for having this site is to promote our Le Tonkinois natural varnish and Flexidisc sander products, we hope you will look at those pages as well as these.

I always appreciate an email if you found these articles useful.

It helps me to gauge how much interest there is and whether it is worth spending a lot of time improving the pages and publishing further items.

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Replace the burner gasket even if it looks in good condition.

We have heard of instances where a re-used gasket looked good but later failed, leaking exhaust fumes into the blown air supply. The only time we would re-use the gasket is when the heater is stripped down a second time within a week or so. Eberspacher D4 heater gaskets are larger than the D2 versions.


When re-installing don't forget to fit the sealing gasket. Do not replace the studs with stainless steel, they cause corrosion. Use locking washers not Nylock nuts, the nylon can melt. Stainless M6 nuts and locking washers are ok. Using Copaslip here seems a sensible choice.

A little tip: If the cable has pulled out of the plastic retaining grommet clean the cable sheath then fix with superglue.

This Airtronic D2 burner looks completely clear of carbon deposits.

Some burners may require chemical or industrial ultrasound cleaning as a mechanical clean cannot reach the hidden parts. Any chemical cleaner can be dangerous, always follow manufacturers instructions.

For health and safety reasons we make no recommendation but many users clean with caustic soda.

The Burner page shows there might be an issue with the older Airtronic D4 burners clogging up plus we have cut one in half to show the parts inside.

Remember to check the glow pin chamber breather hole, shown arrowed, and the fuel inlet under the screen are not obstructed.

Airtronic D2 Glow pin as it was removed. These ceramic glowpins normally do not need any cleaning.

Knobbly deposits usually indicate water in the fuel. D2 glowpin also fits the Airtronic D4.

Unlike earlier models they are designed to last for the lifetime of heater, only replace if faulty.

Eberspacher D2 Heat exchanger and its exhaust port.

Both were clean so no need to clean out the exhaust pipe.

The tiny amount of carbon deposits out of the D2 heater. A 20p coin (roughly 21 mm diameter) shows the size.

The horrific pile of carbon from our older Eberspacher D1LCC that had run on pre 2011 type red diesel.

This is definitely not typical.

Another shot of the D1LCC carbon. This photo included a few large bits that fell out of the exhaust pipe. The central pile was about 7 inches wide.

New screen partially inserted.

Use the supplied tool to push it in carefully as far as it will go.

Always fit a new burner gasket.

The wires are held in place by the ECU, check carefully the ECU is not pushed forward as the fan can catch on it.

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Servicing D2 D4 (1) D5 D1LCC D1L D3L Hydronic Blowers
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However soft deposits can build up extremely fast when a heater fails.

Dereks D2 clogged up after less than 20 hours of use, details and more pictures on fuel problem page

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D2 Burner and heat exchanger clogged with soft fuel soaked deposits shown in the video.

Surfaces covered with a wet coating of fuel. There would also be a very strong smell.

If the user retries starting several times those deposits quickly become saturated with unburned fuel as shown in this video found on youtube     https://www.youtube.com/watch?v=xyoXyUAVrGQ    

Burning as in the video is hazardous, we would use other cleaning methods.


Astounding soft carbon deposits from just 2 days use after heater had been serviced!


The resultant 20 cm (8 inch) wide pile of soft deposits.