Furnace blower runs after temp is reached

If the furnace is cycling on and off and not reaching temp there is a problem in the control circuit. If the thermostat is not satisfied the furnace should be running without shutting off in which case the capacity of the furnace is inadequate because of size or problems reducing the capacity. This could be caused by an increase in home size, poor air flow (dirty filter, loose fan belts, fan running slow, obstructions in the duct), dirty heat exchanger or burner, reduced gas flow, over temperature switch bad causing the burner to shut off early, or a few more technical reasons. You may do well to call a technician to troubleshoot this problem.

Sounds like the heat anticipator in your thermostat is either bad or out of adjustment. Turn of the furnace power. Remove the thermostat wires from the thermostat. Turn the power back on. Connect the white and red wires together. The furnace should start up. Let it run a couple of minutes. Then disconnect the wires. The burners should shut off immediately. The blower will continue to run for 60 to 360 seconds then shut off. If this happens replace your thermostat. If the burners continue to burn, then your problem is either the furnace or the thermostat wires.

Hi Dave. I'm Roger. Its normal for a furnace to shut down completely when the set point on the thermostat is reached. The first and second stages are used when the temp. gets close to set point. The heat output drops to its low stage at around 3 degrees before set point. Check your owners manual for specifics on the fan though.

If it is very cold out and you desire your house to be a certain temperature, you might have to raise your thermostat by 2 degrees to maintain it. Use Liquid Roof for

Check your thermostat to see what your fan switch is set on. There should be two settings - auto and on. If it is set on auto, the fan only comes on when furnace runs. If the switch is set on on, the fan on your furnace is running all the time. Which means when temperature in the house reach what you have set on your thermostat, the furnace kicks off, but the fan keeps running and blows cool air. Some people run their fan all the time, especially if they have allergies, because that's a good way to clean the air.

Sounds like it could be your fan limit switch. Part costs about 20 bucks and is fairly simple to replace. This limit switch is a safety that prevents your furnace from over heating. Usually when your t/s is satisfied the blower runs for a little longer after the burners have stopped, and the reason for that is the limit switch. The blower is supposed to cool this limit switch to a certain temp. and once it reaches this temp it shuts the blower off. Yours is stuck:(


I’m happy to help further over the phone at https://www.6ya.com/expert/george_083af2f0afc0328b

It actually sounds like you may have answered the question yourself. If the mercury isn't breaking contact, then obviously it's still calling for more heat. This is a common problem with the old mercury thermostats and are usually replaced with digital ones that are way more accurate. The are fairly cheap at Wal-Mart and such, and replacing one is basically all color coded.

Is there a setting on the thermostat for Auto or Fan? If so, make sure it is in the Auto setting. You will have a contactor that turns on the elements and a relay for the fan. Follow the wiring diagram to see which relay energizes the fan then unplug it to see if the fan stops.

you have either a bad thermostat or bad controls in the units unplug the furnace make sure the outside unit shuts off turn off the thermostat plug back in if it all starts with the thermostat off you will need service thanks for the high ratting keeps me helping for free.Tom

first off buy yourself a honeywell stat, in my personal opinion lux stats are garbage, I have run into so many that are bad stats !!! but as far as your fan not shuting down, sounds to me like your fan center on your circuit board is bad and will not shut down the fan when needed, you will have to replace the circuit board, as the fan center is a part of the whole of the circuit board, hope that helps