We ran our forced air heat pump today. 15 min. in we noticed it just stopped running. Looking in the breaker panel I could see that the breaker for the heating unit had tripped. When I tried to reset it, with a very loud bang it tripped the main breaker to the whole panel. I reset the main breaker, and tried to reset the breaker to the heating unit and it tripped the main breaker again. I shut the heat pump off and tried a third time, only to trip the main breaker for the whole house again. What gives? Panel problem or heat pump problem?
You should contact an Electrician or HVAC technician. There seems to be a short-circuit somewhere in the circuit supplying the heating unit. DO NOT reset the breaker again until the problem is fixed.
The reason I suspect a short-circuit, is because the breakers are reacting so quickly. If this was an overcurrent situation, the main breaker would likely not trip (unless the panel is severely overloaded).