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Eberspacher Fuel problem - Practical fault finding


Some soft carbon in the exhaust port.

Hard carbon deposits above the screen.

Glow pin screen blackened by deposits.

Vent hole clear but very slightly obstructed.

Small amount of soft carbon deposits inside heat exchanger.

Partly cleaned, deposits were very soft and brushed off easily.

Removed carbon with the old screen to show small size of pile.

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A lot of carbon fell off as the burner was removed and is in a pile at the bottom of the heat exchanger.

Astounding soft carbon deposits after just 2 days use!

The carbon was very soft and most of it fell off when the burner and heat exchanger were separated.

Outside of burner.

End and inside of burner.

Some carbon still on the top of the burner, high ridges have broken off.

The resultant pile of soft carbon after cleaning. It had a slight smell of unburnt diesel.

The pile length here is the same but is more spread out (top to bottom of photo) and photographed from above.

silencer02_big.jpg silencer04_big.jpg

People seem to think we just wave a magic wand and the fault solution appears, not so, we have learnt most of the fault symptoms and can now quickly diagnose many faults but others we need to solve with a methodical approach as with this problem.

In October 2011 Derek's Airtronic D2 failed to start, producing plenty of smoke, so he removed it for servicing and fitted the spare D2. Two days later when that also failed we knew there was a bigger problem. We had never experienced such rapid carbon build up before. With our experience we were able to quickly eliminate some causes but for this article we have added in some of the bits we quickly ignored and explain them in more detail. A third related problem showed up after we thought everything had been solved.

Fault 1

Before starting any fault finding it is very important to accurately identify the heater model number and get as much detail of the failure as possible. Often timing how long till it happens can be a helpful diagnostic. In this case:

Airtronic D2 heater failed to start from cold then automatically switched off. During both the two start attempts fan was running & pump clicking as normal, plenty of white smoke. Heater shutdown completion was about 10 minutes after switch on. This failure sequence was repeated when the heater was manually restarted. Before this the heater had no problems except for smoke increasing on starts during the previous day.

At that point Derek immediately decided a service was required so how did he come to that conclusion?

Note that most of the points mentioned here are covered in much more detail on other pages, including the faults page. The fan running and pump working meant it had passed all the pre-start checks including the glow pin. (see faults page). White smoke is unburnt fuel so some fuel was getting to the heater.

   Shut down after about 10 minutes confirms the Eberspacher has tried to start twice in the normal manner but the fuel has not ignited. The battery is float charged from the mains and those particular fault symptoms give no reason to check the voltage. Eberspacher recommend servicing every year, every two years for low usage heaters. Derek's heater was high usage and often ran for long periods on low setting, sometimes continuously up to 12 hours. We know that this can cause carbon build up and the heater had not yet been given its annual service. Once an Eberspacher gets close to the point of failure and needs a service it usually gets worse rapidly.

So it was reasonable to do a full service. Full 'how to' instructions are on our Airtronic servicing pages.

Pictures are here mainly so comparisons can be made with the replacement heater problem.

Click on images for better quality

Fault 2

Two days after fitting the spare D2 it failed like the original D2. Our first thoughts were that something might have been forgotten like the exhaust pipe not fixed and blocking the inlet or exhaust port. Quick visual checks showed nothing wrong. Diagnostic tests would not help as they would only show failed start attempts which we already knew about. We had quite recently done a number of fuel volume tests for the website fuel pages which involved disconnecting the Eberspacher fuel pipes and measuring the pumped fuel volume using several pumps so suspected we could have caused air leaks. All the connections were tight and the air bubbles in the pipe looked reasonable. A fuel volume test confirmed the pump was ok.

The fuel container showed no sign of water or debris. At that time we had no means of checking the fan speed but it sounded normal. The flexible exhaust pipe had to be removed completely to check it was clear, knocking the pipe on the ground removed a tiny amount, considerably less than a teaspoon, of soft carbon.

The combustion air inlet was clear. The heating air ducts looked ok and were not obstructed. Derek knew that the spare was in good 'just serviced' condition when it was installed. In this case we could eliminate the Eberspacher heater as it had been replaced by the spare but even if we had serviced the original and refitted it we had eliminated mechanical problems during servicing. No electrical fault in our list would cause that fault, it was fairly obvious that it was due to the fuel, combustion and exhaust processes. After a coffee break we still had no idea of the cause so we checked again for leaks as well as doing a precautionary voltage check. We then did another two fuel volume tests in case the pump was intermittent. All tests were ok and the fuel did smell like diesel. We were starting to get desperate. In this situation for us if all else fails we have a coffee break (or breaks), they give us time to think and reconsider.

Having eliminated just about everything else the only thing we had not tested was the fuel, red diesel.

Derek stored fuel in 25L containers and topped up a 5L container from them, he had recently topped up from a full 25L container. The red diesel in that was less than a year old and we had never had problems with relatively new fuel going off before but how to test it? At this point some users would just replace the can with one containing fresh road diesel and do a test. What they do not take into consideration is that the glowpin screen and burner are already clogged so it could still fail. Derek did not want to dump a lot of fuel without proving the fuel was definitely bad so thought up a Heath Robinson type test. Two strips of paper, one dipped in new road diesel, the other in the red diesel, then lit them. The old red diesel strip took longer to ignite and burnt with more smoke, not very scientific but good enough. More information on the fuel degradation will be added on the fuel pages.

The original Airtronic D2 was refitted after a full service and ran ok on the much more expensive road diesel.

One point worth mentioning here is we replaced the glowpin screen on the spare D2 despite the old one only having 2 days use. Once they clog up they usually must be replaced. We might have been able to clean this one as the deposits were soft but decided not to. The gaskets were ok to be reused.

Subsequently we had a third related problem which caught us out but more about that after the photographs.

What amazed us was the state of the spare D2, it had been serviced prior to installing and had only run for 2 days, less than 20 hours. If we had continued to try starting the heater as many users would do the deposits would have become soaked with unburned fuel and been very unpleasant to remove.

A youtube video https://www.youtube.com/watch?v=S9rMigqr0kM shows a saturated burner.

The first D2 had a much smaller amount of carbon.

Fault 3

After everything worked ok for about 3 weeks Derek fixed some bits that had been installed temporarily.

This included the exhaust pipe which was hanging down on the ground and not connected to the silencer.

The Eberspacher was soon smoking again.The only real change had been the silencer. We had thought that with almost no carbon in the exhaust it would not have reached the silencer. We could blow through it easily but put it in some cleaning solution and a lot of black came out into the solution. After cleaning we noticed a row of small holes in the tube inside were now visible, they must have been covered by carbon as we had not noticed them before. That possibly explains why the spare became so clogged, the silencer may have been partially blocked by the first failure. (This was an incorrect assumption, see update below)

Derek had to do yet another service, the screen still looked pristine but was replaced. The problem was finally cleared.

Update to Fault 3 November 2013

David Sheppard cut open a silencer and sent it to us. (see autopsy pages for full pictures and details).

Once we examined it closely we realised the reason for the smoke in our fault 3 was not due to a blockage as we had thought.

Old silencer cut open

This silencer was clogged with limescale.

Upper layer of fibre glass removed.

The holes allow some of the gas & noise to pass into the outer casing area filled with glass fibre, smoothing & reducing the noise level.

We now think the previous fault sent unburned fuel into the exhaust which collected on the fibre glass in the silencer. Then when the exhaust heated up it was not hot enough to ignite the fuel but caused it to be emitted as smoke. If we had left it alone the fuel would have burnt off and the smoke would have ceased after a while. This also explains why the screen was pristine, it had not clogged. Cleaning the silencer removed the rest of the unburned fuel so solved the smoke problem straight away.

Fault 4

There is nothing wrong with relatively fresh red diesel that has not degraded, Eberspacher heaters run ok on it and ours had done so before this fuel degraded. However, fuel we bought to replace the degraded fuel was the same price as the previous year which made us suspect it was old fuel and it turned out to be very poor quality. The supplier probably was still using the same tank of red diesel which had degraded with age but it was not as bad as the fuel in the 25L container which had been stored in bad conditions. The effect of the new fuel was that the Eberspacher would not start first thing on a cold morning. Derek had to start it on road diesel before changing to the red diesel. Once that had been done it was ok, and would start without problems for the rest of the day. We did not expect it to start once the weather got colder and searched for an alternative fuel supplier. We found one who sells Kerosene in small quantities, (28 second central heating oil), and Derek changed to that, it has proved to be the best fuel we have used. After over 8000 hours of use, much of that on the lowest heat setting, his D2 still showed no sign of needing a service.


We learnt a lot during this saga and this page may help by showing how we approach our own problems.

At that time we knew virtually nothing about fuels and fuel degradation so subsequently needed to look on the web for information. I am still not very knowledgeable on fuels but now know the basics I really need. The fault and fuel pages have been updated to reflect what we learned so others can benefit from our experience. We were  thankful we do our own servicing, if we had to pay someone else for the services it would have been a lot more expensive.

It also shows problems that dealers have. Your Eberspacher fails and you take it in and they service it. When it fails within a couple of days you automatically think the service was not done properly.

Lastly the cut open silencer revealed how it was built which enabled us to revise our reasons for failure 3 and shows how we benefit from cutting faulty components apart.

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