Heating system short cycles
On average, your furnace should cycle for about 10 to 15 minutes each time it starts. If your furnace has a bad habit of starting up and then turning off again after a few minutes or even seconds, it is “short cycling.” Here are a few likely culprits for short cycling.
- Heating system too large. While having a large heating unit may seem like a solution to a cold home, a system that produces too much warmed air too fast actually causes problems. When the air around the furnace heats up too quickly, it can prompt the thermostat to end the heating cycle early. As your system starts up and shuts down repeatedly, it strains HVAC components, uses extra energy, and results in more frequent breakdowns. Having your furnace replaced is the only solution to the problem.
- Poor airflow. When dirt and grime fill air filters, airflow is restricted which can strain your furnace or air handler. Your system may overheat, and the internal limit switch may trip. Replace the air filter as soon as it looks dirty.
- Blocked flue pipe. If the flue pipe that routes fumes from your furnace becomes clogged, your system will turn off to prevent CO2 exposure. Keep flues clear and check them regularly for debris. Always keep a carbon monoxide detector running in your home on every level.
- Thermostat problems. The thermostat itself can develop problems, especially if it is older, placed in a location prone to stark temperature changes, or dirty or unlevel. Ask a professional to clean, recalibrate, reposition, or replace your unit if it doesn’t appear to be working properly.
- Incorrect thermostat anticipator calibration. Manual thermostats may have adjustable heat anticipators that increases temperature inside of the thermostat to end a heat cycle early which prevents overheating the space. These older thermostats can be adjusted but may need to be replaced.
- Faulty flame sensor. Flame sensors inside of furnaces detect when a flame is present. and are designed to shut down your entire system if the flame is out, avoiding explosions and gas leaks. Unfortunately, if these sensors become dirty due to soot, they may shut down the system early for safety. These sensors can be cleaned or replaced by a professional if they are the cause of the problem.
- Damaged furnace draft inducer motor. Some furnaces have a draft inducer motor that is designed to expel combustion gases leftover after a heating cycle. If the air pressure switch doesn’t detect enough airflow, it may shut down the furnace. To prevent this problem, keep your flue pipes free of debris. If the issue persists, there may be a fault in the pressure switch or draft inducer motor.