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Why Is My Furnace Short-Cycling?


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Short-cycling is when your HVAC system turns on and off too frequently. The shorter the heating or cooling cycle, the harder your system must work.

Typically, cycles are between 10 to 15 minutes, while a short cycle can be only three to eight minutes, which isn’t long enough to achieve the temperature set on your thermostat before shutting off again.

There are a few potential causes of furnace short-cycling. It could just need a DIY fix, but if you can’t resolve this issue, you should contact a licensed HVAC technician to inspect your furnace to determine if you need a heating repair or replacement.

Dirty Air Filters

If you neglect to change or clean your air filter, all the accumulated dust and airborne contaminants in the filter will make it difficult for heated air to pass through, causing your system to short-cycle.

Your technician will check your air filter during your annual furnace maintenance appointment, but you can also check your air filter yourself. Depending on your filter, you should replace or clean it at least every three months.

Blocked Air Supply Vents

Air supply vents should never be closed or blocked by furniture, but this can cause low airflow, similar to dirty air filters.

The heat exchanger won’t have enough air to transfer the heat throughout your home, and the built-up heat could cause short-cycling. Avoid this issue by keeping vents open, even in unoccupied rooms.

Thermostat Issues

Short-cycling isn’t always an issue with your furnace — it could be caused by your thermostat. If you haven’t scheduled an HVAC tune-up in the past year or longer, you may need to recalibrate your thermostat before considering other solutions.

A thermostat could also kick on or off too soon because of its location — if it’s too close to an air vent, the thermostat will shut off before the remainder of your home feels any changes. It should be centrally located in your home for the most accurate temperature reading. You could also install additional thermostats for more precise heating and cooling zones.

Your technician can determine if thermostat recalibration, relocation, or replacement is needed to stop furnace short-cycling.

Dirty or Damaged Thermocouple

If your furnace’s pilot light goes out and the gas valve is open, natural gas is released into your home. If there is no flame, your furnace’s thermocouple, also known as a flame sensor,  shuts off the gas valve to ensure your safety. 

The flame sensor can become dirty or corroded without routine maintenance, meaning it can’t recognize the flame and will turn off the gas valve, which will cause your furnace to turn off.

An HVAC professional can inspect the thermocouple to determine if it needs cleaning or replacement.

Blocked Flue Pipe

Also known as an exhaust vent, the flue pipe is on your roof. Debris, like leaves, dirt, bird nests, snow, soot, and more, can end up inside the pipe.

If the exhaust vent is partially blocked, your furnace will have enough airflow to start a heating cycle, but safety controls will shut down your heating system to prevent combustion gases that couldn’t escape through the exhaust vent from leaking into your home.

Your heating system will try to start a cycle three to five times before it has a hard shutdown and will need to be reset by a professional. They can also inspect and address your blocked flue pipe.

Improperly Sized Furnace

A furnace’s capacity for heating a home depends on the furnace’s size, so if none of the other issues are causing your furnace to short-cycle, your unit might be too small for your home. Oversized units can also cause problems like high utility bills, so your system must be appropriately sized for your home.

The only solution to an improperly sized furnace is to replace it. Your technician will ensure your new unit is a good fit using:

  • Your home’s square footage
  • Your climate zone (Grand Rapids is in Zone 5)
  • Your desired efficiency (measured by the AFUE rating)

Stop Furnace Short-Cycling With Grapids Home Services

If your furnace short-cycles, you probably won’t be happy when you see your energy bill. Save time and money and avoid the headache of a furnace breakdown with routine maintenance and fast repairs by our highly skilled HVAC technicians.

Is your furnace short-cycling? Call (616)-453-1099 or contact us online to schedule service for your Grand Rapids, MI, home.

We Are Here for You! Contact Us Today.

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