Same result! Take off lower external air vent to access rear of fridge and confirm combustion shroud hot - it was!

Released stat knob in any case, and gas went off. Manual spark ignition, so turn on fridge, turn stat to max, simultaneously depress stat knob for gas and igniter for spark, hear sparking and, eventually, hear gas ignite, watch gauge indication to confirm ignition before releasing stat. But had to set the temp to 30C to provoke firing! :-D Next up, fridge. All connected and turned on, then flush out air. I was fettling the van in preparation for a forthcoming trip, and was 'doing' the gas bits. This is prompted by something I discovered yesterday by being silly! :-) Is it a manual energy selection version, or possibly an AES fridge that has been set to manual. (Presumably you’ve confirmed that he gas stop-cock for the Truma heater is in its fully open position.) So you might be looking at an inoperative or blocked gas valve on the heater. The ‘combi’ #121 error code suggests that no gas is reaching the heater As the fridge will cool OK on 230V (suggesting that its cooling system is operating correctly) it OUGHT to cool on gas too.

If the fridge will light OK and stay lit on gas, I suggest you give its flue and gas-burner assembly a damn good clean and see if that does any good. It’s possible that your old gas pigtail might have degraded internally and the resultant ‘muck’ got into the gas system (the ‘phthalates’ theory that was put forward in the mid-2000s to explain why Truma bulkhead-mounted regulators were failing) and it used to be widely reported on French motorhome forums (well before the Truma reguator debacle) that ‘oily residues’ in bottled gas used in leisure vehicles could disable the burners of the more complex gas appliances like ‘combi’ heaters and fridges. I recall that - in April - you mentioned various problems you were having with your La Strada Trento (but I don’t think its age was ever stated)

Does a piezo igniter need a battery