I have a 5 year old Carrier (#58sta/stx) gas furnace/electric fan. The fan runs continually with no heat unless power is cut off at the breaker. The thermostat is inoperable (digital screen blank w/no back light) though it has 12 volts of incoming power. Waiting for a new thermostat but with the old thermostat removed and no wires touching, the fan still continues to run with no heat. Normal? Is there a reset control on the furnace? Think a new thermostat will return functionality? Is there a way to test the old thermostat with a multimeter? Thanks very much.

I believe you need 24 volts to operate the system and thermostat. Sounds like the roll out safety or other safety device has tripped if the furnace is so equipped.