Normal heating systems don’t run constantly, but instead, cycle on and off several times an hour. However, when your furnace is shutting off much more often than usual, that spells trouble.
This type of furnace problem is called “short cycling.” Let’s look at 4 common causes.
If your air filter clogs with dirt, the airflow to the heat exchanger becomes restricted and the component overheats. This, in turn, triggers the high limit switch (your safety shutoff).
To solve this problem, just turn off the furnace and change the filter, if you have the disposable type. Permanent filters, which do a better job of protecting your furnace and are more eco-friendly, are designed to be cleaned and reused.
Whichever filter you use, be sure to inspect it monthly and change or clean it every 90 days minimum.
For even better airflow, open some of your vents and have your furnace blower wheel cleaned.
Check your thermostat to determine if it is turned on. Make sure it’s switched to “HEAT” and set at the correct temperature. (If the temperature setting is too low, your furnace will shut off more frequently than you’d like.)
Consider thermostat location as well. It should be positioned away from sources of heat or cold (like sunny south-facing windows or drafty doors) and mounted about 1.5 metres above floor level.
Ensure it isn’t mounted too high because, as you may remember from science class, hot air rises. If the thermostat registers extreme temperatures, a shortened furnace cycle may result.
Another possible problem could be that the thermostat is malfunctioning and not sending a signal to your furnace. Check this out with a buddy. One person should stand next to the thermostat, the other next to the furnace. Slowly raise the thermostat setting and listen for a noise from the furnace. Lack of any sound indicates that you may need professional thermostat repair or replacement.
The gas furnace’s flame sensor is a safety device, which cuts off the supply of natural gas when no flame is detected. If your flame sensor becomes choked with soot or corrosion, it can’t function properly and will keep turning off the gas valve.
If you suspect that you have this problem, get expert furnace repair as soon as possible.
Your furnace may simply be too large for the size of your home. An oversized furnace will heat the space too quickly, shut off, and abruptly start again when the house cools down.
This stopping and starting is not only annoying, it also wastes energy and wears your furnace out faster than usual. Furthermore, your home is never really a consistent, comfortable temperature.
The best solution is to replace your furnace with a correctly-sized, energy-efficient model, especially if it’s over 15 years old.