E621H Fault Code Corinium Duo

Hi. I have recently experienced an issue with the Truma CP Plus  control panel having lost all functions which transpires that the rotating knob had, over a period of time, become depressed, so no longer acted like a switch. This was resolved by taking the knob off, resetting the boiler and carefully relocating the knob to allow it to function as a switch again.  I thought all was ok, the screen and functions reinstated, however an error code of E621H appears on the screen and despite resetting the control panel and the boiler, still appears. This appears to render all functions out of action. Whilst heating is not required throughout the summer, I do require hot water. I know, from recent experiences that finding someone that will look at it before August is a seemingly impossible task, I would like to have a go myself.  The fault code E622H points towards either the room temperature sensor or wire. I am a little doubtful that there is a part failure, and feel that it maybe a setting issue. I would be grateful if anyone could advise as I am planning on going away tomorrow for 2/3 weeks.
Many thanks
David

Have you tried pressing the microswitch reset button on the printed circuit board (PCB) on the top/back of the Combi?

I have had that fault a few times and the cure was to simply unplug and re-plug in the tiny plug at the back of the control box, for which you probably have to remove a plastic cover behind it. One of the causes of the fault is simply the loss of electrical connection between the control and the boiler. Try also unplugging / replugging the boiler end as well.

The fault is for the room sensor. So check that the two wire plug going in to the panel is the correct way round and tight.
 If you are happy and the problem is the same you could try reversing the two green wires (thermostat) on the rear of the boiler the press the reset button next to the wires.

The only error code I have had is when switching on the truma  with the sargent control  panel turned of

I can't remember which motorhome I had at the time, whether it was an AutoSleeper or Other Brands Are Available but I had a room heating fault and I diagnosed it to be the room temperature sensor. Being a gas boiler sort of bloke I thought "I think I've got one of those in the garage" so I went and found it, fitted it and the heating worked. They are simple £3 things you can fit yourself, don't go paying £50 for one (? plus £100 fitting charge) . They are pretty universal, used in central heating boilers all over the world, not special to motorhomes or any particular manufacturer. You will probably find it behind a dark brown button with little holes in it on the wall somewhere. Ping off the button and there it is.
https://www.amazon.co.uk/Waterproof-Digital-Thermal-Temperature-Sensor/dp/B01EZZS76E/ref=sr_1_5?dchild=1&keywords=ntc&qid=1624951755&sr=8-5

Hi David
Did you resolve this issue, and if so how? I have the same issue.  Thanks

I seem to remember having that code on mine and all it required was to go in the wardrobe, remove the cover off the back of the control box, unplug the little multi-pin plug, wait five seconds, plug it back in and off it jolly well went, as Jimbo would say. I did also have the thermostat fault as I posted earlier, but that was another occurrence.