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What to do When Your Furnace Won’t Shut Off

by | Dec 25, 2023 | Central Heating

Don’t be panicked, a furnace can easily be shut off. Sometimes furnaces run too frequently, and this can be cause for concern. It may be best to shut your furnace off, and assess it for repairs.

If you don’t know how to shut off your furnace, don’t worry, we’ll walk you through the process, and explain reasons why your furnace won’t shut down.

Shutting off your furnace

Start with switching thermostat temperature setting well below the current room temperature. If this does not work, flip the power switch to the furnace. This is known as the furnace disconnect switch and can sometimes look like an ordinary wall switch.

If you cannot find the furnace power or disconnect switch, turn off the circuit breaker to the furnace at the main circuit breaker box. Generally a furnace will be on a dedicated circuit.

If you smell any gas near your furnace, shut the gas valve feeding your furnace off. If you cannot find the gas valve, trace the gas line backward from the furnace. Generally it will be a 90 degree turn to shut off the gas.

If all else fails, contact a local furnace repair company to sort out why your furnace won’t shut off.

Reasons why your furnace won’t shut off

There are various reasons why a typical home furnace will not shut off. Here are some of the most common reasons.

Incorrect fan settings

One of the possible reasons is incorrect fan settings. Sometimes the furnace is not running, but sounds as it is, because the fan or blower motor continues to run. If this is the case then you may to check the fan switch on the thermostat to ensure the correct fan setting is in use.

There is a possibility the fan has been set to run all the time.

Your thermostat will have settings for the fan, generally AUTO is where it should be set, rather than ON.

Faulty thermostat

If your thermostat is faulty it may be reading the wrong room temperature. This means it will send signals to your furnace to stay on past the set temperature point.

This could be cause by a loose wiring connection, and you can tighten the wiring. You can try to reset your thermostat. Depending on the type, this can be a simple process.

Dusty or clogged air filter

Forced air furnaces move air through filters, that remove dust and dirt.

When filters become dirty, the air flow is limited.

This limited air flow causes your furnace to run harder than needed.

It can also reduce the amount of tempered air flow to your home through your ducts and vents.

Consider replacing the dusty air filter behind the access panel with a new filter of the same dimensions and quality.

Damaged primary controller

The primary controller is responsible for maintaining operation of the main heating element. If the controller stops operating, or is damaged, the furnace cannot regulate temperature.

This may ‘trick’ the furnace into running on when it doesn’t need to.

Damaged ductwork

If the ducts serving your home’s heated air are damaged, then your furnace and blower will need to work extra hard to serve your home with heat.

Improperly sized furnace

An improperly sized furnace will need to run overtime in order to serve your home the heated air to the desired temperature.

Is it safe to shut off gas to furnace?

Yes if the furnace has been shut off already, this will reduce the risk of any furnace accident when the system is off.

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