Low battery voltage can cause this error. To troubleshoot it, turn on the vehicle engine or plug in the camper to 220v supply to have sufficient battery voltage. If the heating works normally now you have used up too much camper battery without recharging , driven with the battery disconnect switch on. If none of above applies, the battery might need to be replaced, report the problem to our rental station.
Please check also the manuals:
Motor Home 4 Heating system and water heater manual and troubleshoot
Motor Home 5 and 6 Heating system manual and troubleshoot
4x4 Comfort with Propex heating system manual and troubleshoot
4x4 Adventure, Comfort, Rayzr, Premium and Luxury with TRUMA heating system