My dads totally sick, so Im trying to fill in but we dont specialize in HVAC or any one type of service, more overall general stuff. Right now Ive been trying to fix this guys electric funace and I dont know what else could be causing it not shut down. I replaced the blower relay, the sequencer, and the thermostat. I fixed the original problem which was the heater coils would energize but the blower would not turn on. But now the furnace will not stop heating after the thermostat turns off. This happens at random, sometimes it shuts down and sometimes the blower & heater keep running. Also if I switch the fan to the auto position (which is high speed) it will trigger the furnace to shut down. The furnace is electric and 25 years old. Does anyone know why it wont shut down?