Truma motorhome Combi 6 Boiler Error E81H Problem Solved

Disclaimer :: Do not attempt this repair unless you are competent. Take your motorhome to a service agent with the appropriate competence.

If you just want the solution without all the reading and photos here it is.

Deep inside the Truma Combi Boiler unit is a gas burner, the flame is ignited by a spark that passes between two electrodes. The electrodes sit in the flame so they are eventually damaged by the heat and have to be replaced. Watch the first 10 seconds of this video and you will see the electrodes are heated by the flame and get red hot. (The video is in German but you don’t need to understand the words to see the electrodes heat up).

The Problem with our Truma Combi Boiler in our motorhome for space heating and hot water.

We noticed that our Truma Combi boiler unit in our Hymer B544 occasionally tripped out with an error message, usually E81H. Pressing the button on the control unit seemed to clear the fault and the boiler restarted. As time went by the fault was shown more frequently and we were having to reset the boiler several times before it would light. 

My background is in Chemical Engineering where we often had complex problems to solve. Many times the real cause of the problem was not what one expected, and that’s the case here. I knew that the gas supply was good, because the cooker and fridge both worked properly using gas. So something was preventing the gas from being ignited, rather like a petrol engine. If it doesn’t start and there are no mechanical problems then it’s either lack of fuel or spark. Same logic here, gas is OK so the problem is likely to be lack of a spark.

I spent a long time investigating the spark, even making a special test jig with a spark gap to demonstrate that the spark was produced at the appropriate time during the boiler start-up sequence. As far as I was concerned that meant the electronics part of the Truma Combi 6 were working and going through their normal operation.

After a great deal of searching the internet and reading forum articles I found a vendor on a well-know internet auction site who offered a testing service for the main circuit board in the Truma boiler. After a couple of emails discussing the problem he said he did not think the electronics was the problem and that some other part of the boiler was at fault.

What next?

I called various Truma agents within a reasonable travelling distance and was very disappointed to discover that they were extremely busy, the soonest I could get the problem looked at was 4 months wait. Not really what one wants to hear. Cost was also a potential problem, £75 an hour was the labour rate at the time, and I was told that it was extremely difficult to diagnose this type of fault and that 2 to 3 hours work for diagnosis was to be expected, then there would be the cost of parts and labour for the repair itself if that was possible.

The cost of a complete replacement Truma Combi 6 was around £1,400 at the time, so I was contemplating replacement of the whole unit.

Eventually I decided after several days of trials and work of my own that the spark electrodes were the most likely cause of the problem and decided that they should be replaced.

Here are photos showing the state of the spark electrodes before and after replacement.

Advice

If your Truma 6 Combi as frequently tripping out and restarts after clearing the E81H error message then it could be the spark electrodes that need replacement. Don’t try to do this yourself, it’s a job for someone with the right competence, grit your teeth and armed with the knowledge gained from this article consider getting the spark electrodes replaced. Of course it could be a different problem, but I can’t help that, I can only relate my experience and hope it helps someone else.