Recently I noticed my thermostat was blank. I check our heater (forced air Carrier) because it gets its power from there. The 5 amp mini-fuse was blown so I replaced it. The thermostat came on briefly but went out again. I had the mini-circuit breaker tested and half of it was bad, so I replaced that but it is still not working. When the heater was working, the mini-circuit breaker had a "hum" indicating it was getting juice. Since the fuse incident, it no longer has that hum. I've had the breakers in the garage tested and they are good. Any clue as to why the mini breaker is not longer getting power?

The transformer might have burnt up.