The heater does not have 12 Volt power supply or there is no connection between the heater and the CP plus control panel.
The power supply to the heater may have been interrupted by switching off the vehicle control panel (not the Truma heater control panel).
The control panel is used to control all other functions in the vehicle and it also switches the power supply for the consumers in your vehicle on or off.
In this case turn on the control panel in your caravan to reestablish power supply for the heater.
Once the power supply is guaranteed and the warning is still present, check the cable connection between the heater control panel and the heater.
Tip for Combi D:
If the laid TIN cables exceed an overall length of 12 metres, this can lead to a fault in communication with the digital control panel (W255H). The “Control panel cable coupling” accessory is the answer here.
Please place this coupling between the TIN bushing on the heater and TIN cable. If two TIN bushings are in use, it does not matter which of the two TIN cables is used by the coupling.
The “Control panel cable coupling” part can be ordered from our specialist dealers (part number 39050-00175).