Kemerton XL

I have mentioned this previously and the van has been into the dealer, but fault is not rectified,
If the van's heating is set to 'off,' with the van plugged in and internal Harmony power 'on,' the blower blows cold (ambient temperature) air on full if left for a period of time. Fault code W255H displays, which seems odd as that usually means no power connected (which it is) and heating on electric. If I turn the power off at the panel the blower stops. I switch back on and blower is off - until after a period of time when it starts again.
The only way for the fault not to occur is to set the heater to a low temperature. I have been setting it to around 7 degrees in this warm weather and no fault.
Any more thoughts from anyone?

In my 2014 wxl the truma system can be set to blow cold (ambient) air through the vents, I don't have the harmony system fortunately, the control for this function is the furthest right logo on Truma control panel, ie van heating,  then hot water etc. Look for fan symbol, and turn down to zero, should be explained in instruction manual.

We have a 2019 Kemerton XL. I would suggest if you have not already done so to contact the Truma help desk. I haven't got their number but in perhaps 2020 I used their number in the Harmony manual and Rachel was helpful. She identified the reset button behind the black slide off plastic cover on our Truma unit. This action helped then.
This was at a time when Sargent had supplied defective EC700 systems to A/S, hardware, software, who knows both crap? Sorry it cost us £££, miles of travelling and many hours when we should have been using our van for holidays rather than visiting Sargent in Beverly, our A/S dealer a few times and Willersey.

We haven't experienced the fault you have, yet.

Oh yes, of course the fan can be set to run in order to provide cool air circulation. However, the fan is switched to off when this fault occurs.