I don't think that is correct. I would suggest that you locate the model number of the heater and download the installation/operation manual for the unit. It will give a description on how the unit should and a wiring diagram to help trouble shoot the problem. Sounds like you may have a relay to the motor that is sticking in the closed position.
1998 Rexhall Anthem 34' DP, Cummins ISB, Allison 5 speed, Spartan Chassis, 300 watts solar.