We are having a problem with our Truma water heater when operating in electric mode. The water heats up but then the heater cuts out after reaching temperature. It will not re-heat until the heater has been turned off and left for a period. I am assuming that this is a fault with a temperature cut out/thermostat switch. can anyone help with suggestions as to where I should start to look. We are currently out on a site in Portugal. Incidentally the heater works perfectly on gas.