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Is Your Furnace Short Cycling?


Does your furnace click on and off repeatedly before reaching the desired temperature on the thermostat? Does it shut off before blowing any warm air through your home? It may be that your furnace is short cycling. It’s a common problem for homeowners in colder climates and if not diagnosed properly and corrected, it can lead to higher utility bills, expensive repairs, or even an unexpected furnace replacement. Let’s take a look at some possible causes of furnace short cycling and what you can do to prevent unnecessary and costly repairs down the road.

The air filter is dirty or clogged.

One of the most common reasons for short cycling is a dirty or clogged air filter. Clogged filters restrict airflow, which affects the exchange of heat in your home. When the furnace is on, constricted airflow traps heat inside the system, causing it to overheat and eventually shut off prematurely. Changing your filter every three months, or sooner if you have pets or allergies, keeps air flowing freely and your heating system running smoothly during the colder months.

The thermostat is faulty.

The second most common issue with a furnace short cycling is the thermostat. As with all electronics, thermostats can go bad over time. If your furnace keeps turning on and off, this may be an indication of a malfunctioning or broken thermostat. There are several things that could cause your thermostat to not function properly including faulty wiring, dead batteries, or the location of the unit. Placing your thermostat too close to a vent or other heating source may cause it to cycle on and off at irregular intervals. Unless the batteries on the unit need to be replaced, it’s best to contact an HVAC professional to move the thermostat or replace the wiring if necessary.

The furnace blower isn’t working properly.

The furnace blower is the mechanism that circulates air throughout your home. Typically, when the blower motor is damaged or broken, the furnace won’t turn on at all. However, in the rare instance it does, no air circulates over the heat exchangers, causing the unit to shut off repeatedly. To test the furnace blower, hold your hand over the vent to check if air is coming out. If there is weak or no airflow, most likely there’s a problem with the blower. Contact your heating systems professional right away to repair or replace the blower.

The flue pipe is blocked.

Also known as the exhaust vent, the flue pipe can cause your furnace to short cycle. The flue pipe is located on the roof and can become clogged with dirt, leaves, branches, and even bird or other animal nests. This may lead to a buildup of hot gas in your furnace and cause it to shut down if it overheats. Have your flue pipe inspected during routine maintenance appointments.

The furnace isn’t properly sized.

If your furnace is too big for your home, it can cause the unit to short cycle. An ill-fitted unit can cause your home to heat too quickly, then abruptly shut off. Once the home is cold again, the cycle repeats itself. If this is the case, you may have to replace your heating system all together.

If your furnace short cycles, you should contact your HVAC professional right away. Ignoring the problem could lead to major repairs and expenses down the road. A good way to avoid issues with your furnace is to schedule regular preventative maintenance at least once a year.

Family-owned and operated since 1980, Heating & Cooling Two can help service all of your HVAC needs. Contact us today to schedule a repair or routine maintenance.