What is Short Cycling on a Furnace

You can say your furnace is short cycling when it doesn’t reach the required temperature before returning. For instance, if you set your thermostat at 73 degrees, but the furnace stops at 65 or 58 degrees falling short of reaching 72 degrees, your furnace is short cycling. Another meaning for short cycling is when the furnace occasionally goes off and on. Some furnaces run for several minutes to reach the controlled temperature before turning off. A damaged furnace may experience this cycle frequently or shuts down after running for some minutes.What is Short Cycling on a Furnace

What Causes Short Cycling?

Furnaces come with safety systems that control the starting of fires, carbon monoxide, or gas leaks. Short cycling is primarily caused by the fan limitation, installed to prevent fires and damage to the furnace. An efficient furnace comes on and off between three to eight times per hour, emitting a heating cycle of seven to twenty minutes.

But when it happens too frequently, your furnace is faulty. Short cycling also has an advantage because it proves that the machine mechanism works efficiently and prevents severe damage from occurring, such as fire. However, before starting any repairs on the furnace, ensure you understand how the equipment works. Basically, the machine has a fan or blower that circulates the air in the heat exchanger and fuel through the tubes and then into the rooms.

The machine is designed with many safety precautions to prevent the machine from acting in an unsafe manner. The furnace is programmed to turn off if it becomes too hot and to shut off the flue limit if the venting system is not working efficiently. Several conditions can cause a furnace to shut down, such as

  • A faulty thermostat – a faulty thermostat does not operate properly, leading to the furnace’s short cycle. The fault could result from a bad battery which is expected to be changed every six months.
  • A clogged air filter – a clogged filter blocks the blower from efficiently circulating the air through a heat exchanger. The problem can lead to overheating the exchangers affecting the fab limiter, and turning off the system.
  • A clogged flue – the flue or vent pipe can get damaged either due to an object obstructing its flow or a pest like a bird or a rodent nesting in the furnace. The furnace will turn off to prevent the emission of carbon monoxide poisoning and other damages.
  • A dirty flame sensor – the flame sensor or thermocouple is designed to alert the device in case of flames and to circulate natural gas. A dirty flame sensor or damaged thermocouple affected the gas valve shutting down the appliance to prevent natural gas from accumulating to prevent fire.
  • A damaged igniter – the hot surface igniter or pilot light may not function properly, leading to the short cycling of the furnace to prevent gas accumulations.
  • A fan limiter failure – the fan limiter is installed to prevent the heat exchanger from getting too hot to prevent fire or damage to the system. Any crack in the appliances may lead to the emission of carbon monoxide. If the fan limiter is damaged, the system shuts down prematurely.

For more information on furnace service, short cycling or other furnace repairs, please contact Pilchuck Heating right away. Now is not the time to have your furnace go out. Contact us or schedule a service here.

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