Does yours have a separate switch on the dash?
Does it have a separate circuit breaker in the main panel, since it is 120 volt you have to be plugged in or running the generator.
Mine has an outlet wired at the rear of the coach, the block heater plugs into that. During travel we leave it unplugged as road dirt moisture gets into the electrical outlet.
Finally, we have a switch on the dash for the block heater, the switch is 12 volts. It actually provides a signal to a 12 volt to 120 volt relay that turns the block heater on. That relay could go bad.
The problem is you don't know where this relay could possibly be hidden, in my case it is behind the main electrical circuit panel and the only way to get to it is to take the EMS panel front out, not an easy task.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi