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Purl's Sheet Metal & Air Conditioning Blog

Why Won’t My Gas Furnace Turn On?


This isn’t a situation you want to run into when the outdoor temperatures drop. A gas furnace not heating can happen for multiple reasons, some simple and easy to correct with troubleshooting, others that require calling professionals like ours to handle repairs.

We’re going to look at some of the common causes for a furnace that won’t turn on and provide heat to a home. Although we’ll point out situations where you can remedy the issue on your own, we want to stress that any actual repair must have a licensed expert. Tinkering with a gas furnace on your own can be extremely hazardous. When you have any doubts about your gas furnace, please reach out to us rather than attempt to solve it yourself.

The furnace switch is off

The first thing you should check if your furnace isn’t coming on at all is the furnace switch. This is a dedicated power switch for the furnace that’s located near the cabinet, used to shut down the furnace during the off-season and in case of emergencies. Make sure the switch is turned to “on.”

The furnace has lost power from a tripped circuit breaker

Yes, gas furnaces require electricity to run (electrical ignition system, blower fan, control panel), so if the circuit breaker for the furnace trips, the furnace will not turn on. Check the home’s electrical panel to see if there’s a tripped breaker. Reset it and see if the furnace comes back on.

Loose cabinet door

As a safety feature, most modern furnaces will not turn on if their cabinet door is open. A loose cabinet door can cause the furnace to register that the door is open and not turn on. Open and close the cabinet door to make sure that it’s fully closed.

Faulty ignition system

The standing pilot light in gas furnaces has been almost entirely replaced by the electrical ignition system. If the igniter breaks, a safety feature called the flame sensor will detect that the burners haven’t ignited and shut down the furnace. You will need to have technicians replace the failed ignition system.

Faulty furnace limit switch

The limit switch is an important component that helps the blower and burners work properly together in the furnace and to monitor that the furnace isn’t overheating. If the limit switch malfunctions, it may prevent the furnace’s blower or burners from coming on. (Conversely, it can cause the blower to run nonstop.) Never tamper with any of the furnace’s safety features: call for technicians to look into the situation.

Thermostat failures

The problem with the furnace may come from a thermostat malfunction. If the thermostat is incorrectly registering a hotter indoor temperature, it won’t activate the furnace when you expect it to. The thermostat may also lose its connection to the furnace’s control panel and not be able to signal it to come on. Technicians can repair or replace the thermostat to fix this. 

Clogged gas line

Blockage in the gas line can stop gas from reaching the burners. If this occurs, the flame sensor will soon shut off the furnace as a safety precaution. Always leave work with the gas lines to professionals.

Contact Purl’s Sheet Metal & Air Conditioning for furnace repairs. Uncompromised Quality & Customer Service Since 1952.

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