You may know this but if not, do not plug in or out of shore power whilst the heater is working. It will send a spike and blow the control unit of the heater. This is the advice I have had from my service centre who are dealing with a lot of boat units at the moment. No problem with trucks of motor homes so this is the only thing they can suggest. My unit blew as did my friends and we came to the same conclusion.
Keith Carole Wave Dancer