Truma Combi 4E Fault

I have a Warwick Duo 2011 which has a Truma Combi 4E boiler.
All was working well on gas (no power hook up) until it stopped working and the dreaded red light lit up on the two dial control panel. So no heating for 5 nights and no hot water for a shower!
I'd already removed the plastic panel covering the fuse and 12 volt wires and tested for continuity and couldn't find anything at fault.

Back home I set too to investigate.
The first thing I did was to remove the same plastic cover exposing the 12 volt fuse and part PCB board.
Next I removed the plastic grill (top centre of boiler) to expose the Combustion Air Motor with small axial flow circuit board cooling fan. Slide plastic grill upwards.
Last I removed the plastic grill cover over the centrifugal fan which blows heated air into the living space. Remove using a flat headed screw driver to prize off. To get at this fan I removed the plastic circular air vent in the under bed unit by pushing out despite being a tight fit.

I tested on gas winter operation only as I'd drained the water. - Both the above fans started to rotate for a few seconds though the Combustion Air Motor tended to oscillate back and forth. The red fault light came on, fans ceased to rotate and a small red LED light started flashing on the PCB board.
I carried out the same test on mains electric and the same things happened and the same LED red flashes.
So, the fault was identical on gas or electric.

The red LED flashes a fault code of short and long flashes. Counting the flashes and comparing with a Truma fault code chart I'd downloaded told me that my fault was with the Combustion Air Motor at nearly £300 !
I removed the Combustion Air Motor which, hidden from view inside  the boiler, has has rather sophisticated fan which presumably blow out gas exhaust gasses and brings in combustion air.
I was a little confused as to why I got the same fault code on mains electric but then realised the boiler can be operated on both gas and electric at the same time so perhaps this fan unit operated all the time even if no gas was being used.

After 10 years use with no maintenance I found the centrifugal room air fan severely clogged up with dust and fluff which I painstakingly set about removing with a pair of tweezers one blade at a time so as to avoid dropping the clogged bits inside the fan housing. Was this clogged fan causing the unit to overheat I wandered although air did get blown through the space heating vents. This fan is very difficult to get at hence the use of tweezers.
Also, to remove the Combustion Air Motor I partly removed the water pump to improve access to removing its three screws taking care not to lose any screws inside the boiler.

Disconnected cables must be replaced in exactly the same manner so as not to mix up polarity. Take pictures if this helps.

So I'm writing this in case anyone else has had a similar problem. Did you pay the full price for a new Combustion Air Motor or get a second hand or refurbished one would be useful to know as they are not cheap ? Did replacing solve your problem ?
I'm also sharing this experience to suggest that perhaps cleaning out the centrifugal fan every year or two would be good maintenance practice. Why doesn't Truma and/ or Auto Sleeper recommend this ?

I did telephone Truma to get confirmation concerning the fault codes. I suggested that perhaps I could replace the Combustion Air Fan myself at which they advised that I should seek 'expert help' as their 'duty of care' responsibility. It seems removing three screws and the fan is high risk business !!

So I am about to source a supplier this week but would welcome advise in this respect or any related to my Truma fault. 

I had Truma replace my fan during lockdown. As you say - £300 plus of which the vast bk was the appalling price of the fan.

Progress I hope.
I've been in touch with A&R Electronic Developments Ltd of Cannock and they will test and if need be repair the circuit board components for £95 (£30 test only).
They can also test and repair the PCB board if required.
So I'm posting off tomorrow and hopefully it will come back ok !
A&R did confirm that the Combustion Air Fan did work on both gas and mains power hook up, or that the same fault occurs on both power sources.

We'll A&R repaired my Combustion Air Motor as promised for £95 + P&P. Posted it Wednesday, rang me Thursday to say it was faulty and he's fixed it, returned that day and got it back Friday.

I've fitted it, tested on electric and gas and all works fine.
Things to realise are ... CAF works on both gas and electric. On electric any setting only the green PCB LED lights up. On gas any setting, on start up first green then amber as it starts to ignite, then red when ignited. So on gas Truma confirmed all three LED lights lit including red.

I think any DIY capable person could fix this issue but care is needed taking the three screws out and replacing them and care with any driver bits you use. Slow and easy is the way.
For just over £100 it was all fixed.

Thanks for letting us know the outcome. Can you describe where on the boiler the air combustion fan can be located. I guess it's too late to post a photo 

It's located top centre of the boiler at the front, opposite end to the warm air duct outlets.
It's behind a removable plastic grill. Slide up to remove and you will see a small propellor like fan behind which is a small circuit board. Behind the circuit board inside the boiler is the Combust Air Fan. It's all one unit held by three star screws.

The only other fan is for the room air and is multi vaned centrifugal type situation bottom right at the front of the boiler. Prise out grill with a screw driver to clean.

Many thanks for that, I will take a look to see what the access is like