This is an older furnace.It works fine sometimes! I raised the tstat and nothing happened, I pushed the fan switch from auto to on and it worked-back to auto and it didn't work. When I checked the breakers and flipped them off and back on the blower started.Any idea where the problem may be? Thanks,BarbS

Sounds like the blower relay for heating. Most furnaces have separate windings for high and low speed blower. Heating uses a slower speed that On or A/C. The windings are each controlled by a different relay. The sequence is, the gas comes on, later by a timer or limit switch, the blower comes on, and if it doesn't, another limit switch shuts off the gas. If the blower is already running, the gas will come on and stay on until the thermostat shuts off. If you are lucky, the old furnace doesn't have the relays on a circuit board. Follow the wires from the blower back to a little box with 4 wires, one from the blower, one from the house wiring, one from a transformer, and the fourth from a limit switch. Take a plastic handled screwdriver and put the tip on the terminal that goes to the blower, and tilt it to where the shaft touches the one from the house wire. It may spark a little, it is 120 volts, needing respect. If the blower starts, the motor is OK. Next, use a length of wire to run from the other terminal of the transformer to the fourth terminal. It is only 24 volts. If the blower starts, the problem is the limit switch. If it doesn't, it is the relay. Remove which ever, and take it to an electrical shop and let them find the right new one.

If the furnace has a circuit board, the above tests, and replacing the relay are much harder. A whole new board is much more expensive.

Thanks for the quick response! This is an Intertherm electric Model FEHA-015HA-01 Are your suggestions,to check the same for an electric furnace?
The only way the blower seems to work now is by the fan switch on the furnace. Thanks,again Barb Smith

The electric furnace should work about the same, except having a relay controlling the heating elements instead of the gas valve.

The relay may have gone from flaky to dead.

My son came to follow your suggestions- he was checking wires and connections etc. and decided to wait until a weekday when HVAC stores would be open. Since he tightened and checked all,it seems to be running fine! My only problem NOW is-it doesn't always shut down -it sometimes starts up and shuts down a couple of times before it shuts down for good. Any more suggestions?? Thanks,barb Smith

Tightening the connections may have been enough to bring the relay back from dead to flaky. Yeah, It will be warmer today with the relay partly working than removed. Smart kid.

It helped me narrow my search