Heil furnaces are reliable and accurate, but the risk for breaking down isn’t null. Many things can go wrong with your furnace, and the fact that it has so many components is both a good and bad thing. On the one hand, having many components is how reliable and precise performance is obtained. On the other hand, it’s going to be more challenging to find the cause of a problem. And with so many electronic components, fixing isn’t possible for most homeowners; professional help will be the only solution in most cases.
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Why does the furnace fan keep running?
Several factors could make the furnace running without stopping, but some are more common with Heil furnaces:
Control board
The control features a relay that controls the voltage for every component in the furnace. When the relay controlling the blower motor fails while it’s closed, it will still send voltage to the blower motor. Therefore, the blower motor won’t stop running.
If the control board is defective, you will have to replace it.
Also, the control board fan relay could be stuck or welded in the On position. The fan center relay/control board’s contacts could be welded closed, so the fan runs all the time. Gently tap the fan relay to observe if the fan goes off.
New furnaces come with a control board monitoring the fan off and on timing,
The thermostat
The first thing you want to do is see if the fan isn’t in the On position.
The thermostat features electrical contacts that monitor the power supply to your furnace. When the connection monitoring the blower motor sticks closed, it will still send voltage to the blower motor, making it run without stopping. You may use a multimeter to check the thermostat’s continuity, verifying that it’s not defective. When the wall thermostat reveals a continuity between the R and G terminals, if the thermostat is in the Off position, the thermostat is failed. You will have to replace the thermostat with the same model.
Issues with the rollout switch/high limit
When the furnace goes off on a high limit, or one of the rollout switches stays open, the furnace fan won’t stop running because the control board informs the stove that it’s overheated, so it has to run for cooling.
You need to take a look to ensure that the rollouts and limits are closed. Use a voltmeter for further testing.
Sometimes, the fan limit control or the rollout switches sticks open so that a new fan limit control could be necessary. Many rollout switches come with manual reset, so you only have to press a button on the controller.
The limits and rollouts are safety features for protecting you and your family. You also have to ensure that the limit/rollout is open. It’s common for them to open when your furnace has overheated. The vent may be stopped up, or the heat exchanger could be leaking, and only an HVAC technician could solve the problem.
A new fan limit control could also be necessary, so selecting the proper model is essential.
Check the power
You should also make sure that you’re not using 24 to 28 volts between the Green and C (standard) wires on the control board. Ensure that the thermostat is set to Fan Autor, as the thermostat shouldn’t ask for heating or cooling.
When you have 24 volts between G (green) and C (com) thermostat cables on the control board, the thermostat or its wires could be defective. When the fan is set to On, you should always have 24 volts between G and C.
