Truma E520H error

We have this error code (E520H) on the control panel, reset from panel doesn’t clear it. We see “no reset for 15 minutes, heater locked”. We wait 15, press the reset button on the boiler and red light goes out. Restart from the control panel hear a click from the boiler and red light flashes and error code reappears.

No sign of this code in the manual, or anywhere online?

Any thoughts…and be gentle you are dealing with a non-skilled person here!

Ring up truma they are very good should have an answer

Agree contact truma .
E520 is fault with boiler electronics which requires professional assistance.
Found this info on Truma fault codes Atlantic Caravans during Google search.

Better still on a 2021 model get your dealer onto it.

Problem solved..thanks to my dealer and Truma. Suggestion was that 12v supply was interrupted during boiler startup. To clear make sure the error code is displayed on the panel, then press reset button on the boiler but release it the moment the orange light comes on. There should be clicks as the solenoid operates and the code clears. It worked as described!
Thanks for your suggestions!

It's a shame the Truma manual does not show all error codes and explain how to use the PCB reset.  Truma will say this is only for service engineers but the reality is different.  I was talked through the reset by my dealer over the phone.