When your Truma heating    ” wont work , have tried everything , Manual useless, Truma helpline not available  , try this:

For future reference turn off the truma and wait 20 mins – it then resets itself.
Make sure you turn off at the control before disconnecting gas or electricity otherwise the error code will come on again.

The system has its own close down cycle and if you just un hooked the mains with it still set , this code comes up. In Truma theory it ie the gas supply interrupted , but if you have gas supply , then try this before despair sets in.

This is by design to fulfil the requirements of the Gas appliance regulations which itself replaces the Gas Appliance Directive for boilers from 2018.
The new Truma Combi meets the new gas appliance regulations with extra safety and practical improvements. The Combi has an extra solenoid fitted and the 12 volt pcb now has a reset button.
For end users they will still reset the Combi through the Cp+ control panel for typical field failings. i.e.
• Ran out of gas
• Failed to connect 240v etc
However if they keep pressing reset without dealing with the issue first after 5 attempts the screen will lock out for 15 minutes. This lock out will be recognised by the panel code flashing constantly for the 15 minutes.This should only happen if the panel keeps trying to be reset with first resolving the issue; in that scenario the lock out needs clearing from the reset button on the PCB. Beyond that I’d need to speak to Truma, though you’d want to look at the historical error codes that are present to look for consistency’s – E517H can also suggest faulty parts triggering the failure. Kind regards, Reliance