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Furnace Does Not Heat

The 12 most common part(s) or condition(s) which contribute to the symptom Furnace does not heat are listed below. Check or test each item and watch any available videos. If you are still unable to solve the problem you may need to do additional research and troubleshooting. Remember, with our 365 Days. Period.® return policy you can return any part for any reason. So, go ahead and buy it to try it. No other parts retailer offers this unconditional return policy.


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For the symptom you selected, these are the most common parts or causes, ordered by the likelihood of fixing the symptom.

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Igniter

If the furnace does not heat the igniter that lights the gas burner might be bad. The igniter is energized with 120 volts by the furnace control board causing it to get very hot and glow bright orange in order to light the gas burner in the furnace. If the igniter fails or cracks the furnace won't heat and it will need to be replaced.

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Flame Sensor

If the furnace does not heat the flame sensor might be bad. The flame sensor monitors the gas burner. The flame sensor might not be detecting the flame correctly causing the control board to shut off voltage to the gas valve stopping the ignition process. The flame sensor can sometimes be cleaned with a soft abrasive pad, but will likely need to be replaced if the problem reoccurs.

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Draft Inducer Motor

If the furnace does not heat the draft inducer motor might be bad. The draft inducer fan motor on a furnace draws air into the burner and then exhausts it out the flue. The inducer motor air flow through the burner also closes a pressure switch to signal the board that proper air flow is present. If the furnace does not heat the inducer motor may be defective and unable to close the pressure switch which causes the ignition process to stall.

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Control Board

If the furnace does not heat the control board might be defective. The control board regulates the power supply to the components of the furnace. If the board fails it can cause the unit to not initiate the ignition system correctly causing no heating.

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Limit Switch

If the furnace does not heat the limit switch might be bad. The limit switch on a furnace monitors the temperature of the furnace's heat exchanger. If the furnace filter is clogged or air is not passing through the furnace blower properly the heat from the heat exchanger will not be circulated throughout the house properly and the heat exchanger will get too hot. The limit switch will trip if this happens to prevent further damage to the furnace. When the limit switch trips the furnace will not heat.

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Flame Rollout Limit Switch

If the furnace does not heat the flame roll-out switch might be bad. The flame roll-out switch on a furnace monitors the heat surrounding the burners. If the burner flames are not being drawn into the heat exchanger and the exhaust vented out the flue properly than the roll-out switch will open and prevent the furnace from heating. Poor air flow through the burner is often caused caused by insufficient available air surrounding the furnace or a restricted exhaust vent.

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Wall Thermostat

If the furnace does not heat the wall thermostat might be going bad. The wall thermostat has contacts in it that control the furnace. If the contacts in the wall thermostat fail the furnace will not turn on properly.

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Gas Valve Assembly

If the furnace does not heat the gas valve might be bad. The gas valve for the furnace opens to allow gas to flow into the burners. The control board sends 24 volts to the valve during the timed ignition process. If the valve is defective the control board will send the voltage, but the valve will not open and the furnace will not heat.

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Pressure Switch

If the furnace will not heat the pressure switch might be bad. The draft inducer motor air flow through the burner should close a pressure switch to signal the board that proper air flow is present and the ignition process can continue. If the furnace does not heat the pressure switch might be defective causing the ignition process to stall.

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Other Causes and Conditions

Gas Supply Problem

If the furnace does not heat than the gas supply valve should be checked to be sure it is on. Also, if you have propane then it is possible you have run out of gas if the furnace does not heat.

Other Causes and Conditions

Air Flow Problem

If the furnace does not heat there could be an airflow problem. In order for the burner to stay on and not trip a limit thermostat the furnace needs proper air flow through the burner. Air is drawn into the burner from the surrounding area or from outside the home. If the furnace is located in a utility closet or in a cramped storage room there may not be sufficient available air for the furnace to heat properly *see manufacturers recommendations for proper furnace ventilation. If the furnace draws air from outside the home check for an obstruction at the air inlet.

Other Causes and Conditions

Incoming Power Problem

If the furnace does not heat, check to make certain there is electricity to the furnace. If there is no power to the furnace check the circuit breaker or fuse for furnace. If there is power to the furnace, check the more common items in this troubleshooting guide.

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