Why Does My Furnace Keep Turning On and Off?

A properly-working furnace will automatically turn on and heat your home when it senses it’s cooler than the thermostat setting. It will turn itself off once the specified temperature has been reached. This cycling process keeps your home or building at a comfortable and desired level. However, if the unit keeps turning on and off for no apparent reason it may indicate a problem.

When furnaces continuously turn on and off at random it’s typically because of something called short cycling. If it’s not taken care of it could result in higher heating costs as well as permanent damage to the furnace.

On average, a heating system cycles itself on and off between three and six times each hour. If a furnace is going through this cycle more often it’s recommended that you contact a professional HVAC contractor to have it tested and properly diagnosed. Short cycling can sometimes be caused by something as simple as a dirty or clogged air filter. It’s hard for warm air to efficiently pass through a dirty filter and it backs up in the heating system. The furnace will believe the home has been heated to the desired temperature and will shut itself down. But the house is actually cooler than the furnace believes and it will start itself up again.

The solution here is to clean or change your filter on a regular basis. Also, be sure the filter is for the specific brand and model of the furnace. Short cycling can also be the result of a faulty thermostat. Just make sure it has been programmed to the temperature you want and the battery is good. The position of the thermostat could also make a difference. If it’s located close to a source of heat or cold air such a heat register, direct sunlight or drafty door or window, it may believe the temperature is warmer or cooler than it actually is and the furnace will shut down.

To test this, you can shield the thermostat from the source of heat or cold with something such as a piece of cardboard and see if it halts the short cycling.

If the air filter is clean, the thermostat is programmed properly and is located away from a heat or cold source then the problem lies elsewhere. Some other causes could be a corroded flame sensor, a foreign object stuck in the air vents or chimney or the wrong size of heating system. If there’s reason to believe you have one of these problems please contact us at Lloyd HVAC services of Toronto. One of our specially-trained technicians will be glad to make a house call to help you out. It’s important to have the heating system checked out to make sure you know exactly where the problem lies instead of making an educated guess at it.

There are still a few other things you can check out before calling an HVAC technician. These include having the air ducts cleaned and making sure your air vent registers aren’t being blocked by your furniture or plant pots etc. In addition, there are evaporative air conditioning coils above most furnaces which absorb heat from the air. The system can also short cycle if something’s blocking the airflow in these coils and it can lead to short cycling when either the air conditioning or heating system is on.

Furnaces can overheat and this can lead to short cycling as well. Most newer furnaces are equipped with safety devices which can monitor the temperature. Sometimes the heat exchanger can overheat though and this will cause the furnace to automatically shut itself off. This is designed to prevent damage to the system.

On rare occasions, the furnace may be shutting on and off due to a cracked heat exchanger. If you can’t figure out why your furnace keeps turning on and off we’ll be able to inspect your pilot light and make sure there isn’t a fuel disruption somewhere down the line. We’ll also make sure the fuses and electrical connections are all in working order.

A Lloyd HVAC technician will conduct a thorough inspection of all your heating equipment to find where the problem lies and make sure it’s taken care of so it’s running safely and efficiently. We service Toronto and the surrounding GTA and also offer annual HVAC maintenance plans to ensure your HVAC system runs smoothly all year long.