A furnace is a convenient, reliable way to stay warm during a North Carolina winter, but there are a number of furnace issues that can leave you out in the cold. If your furnace keeps shutting off, it’s important to identify the cause and have it resolved as quickly as possible. Read on to learn some common reasons why your furnace is refusing to stay on, and solutions to restore efficiency and optimize performance.


Short cycling is the action of your furnace turning off and on repeatedly, and can lead to a shortened equipment lifespan, inflated energy costs, and loss of comfort. During normal furnace operation, the unit cycles on when the thermostat calls for heat, and once the desired setpoint has been reached, turns back off. Most furnace issues can be avoided with preventive annual maintenance, including the inspection, cleaning, and tuning of your furnace. Common causes of short cycling include:

Dirty Air Filter

One of the most likely causes is a dirty air filter. Replace or wash the filter as needed, typically every four to six weeks during peak heating season.

Restricted Airflow

A lack of airflow can cause the heat exchanger to overheat, which in turn trips the high limit switch and shuts off your furnace as a safety measure. Reasons for poor airflow include:

  • Dirty air filter – Once air is no longer able to flow through the filter, the blower will be unable to draw a sufficient volume of air across the heat exchanger to cool it down.
  • Closed or blocked supply or return vents – Closing one or more supply vents or placing furniture, draperies, or other items in front of return vents can slow down certain types of blowers and reduce airflow.
  • Dirty blower wheel – Over time dirt can accumulate on the wheel, slowing down air production.

Faulty Thermostat

It may be time to reprogram your smart thermostat to accommodate the changes in fall and winter temperatures. Low batteries, or the addition of a heat-producing item, such as a lamp, in close proximity to the thermostat sensor can affect temperature readings.

Improperly Sized Furnace

A furnace that is too large for your home may short cycle as it quickly heats your home, shuts off, and repeats the process. The experts at Comfort Services will properly size your furnace replacement, to maximize performance and efficiency.

System Malfunction

More serious issues include:

  • Dirty flame rod
  • Cracked heat exchanger
  • Malfunctioning inducer
  • Circuit board malfunction

A certified, licensed Comfort Services technician can quickly diagnose the issue, and determine if furnace repair or replacement is the best option.


The team of experienced, licensed professionals at Comfort Services Heating & Cooling have been providing quality furnace installation, maintenance, and repair services throughout the Raleigh-Durham area since 2004.

Call us today at 919-646-8019 to schedule service, or contact us online and let us know how we can help. 

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