Normally, your gas furnace should cycle on and off 3-8 times hourly, maintaining a comfortable temperature in your home. But a furnace that keeps shutting off every minute or two (or “short cycling”) won’t heat your house properly. Not only that, it may be signalling a bigger problem with your heating system that you need to take care of.
A short cycling furnace is when the heating system turns on and off rapidly and more frequently than it should. Instead of completing a full heating cycle—where the furnace runs for an extended period to reach the desired temperature and then shuts off—short cycling involves the system cycling on and off in quick succession.
So don’t just sit there and shiver. Troubleshoot this common problem and learn how to repair your Toronto furnace. If it’s time to buy a new furnace in Toronto, give Husky a call!
1. Furnace Airflow Is Blocked
Your furnace’s heat exchanger needs a good flow of air to cool it down. If the air flow is obstructed, the heat exchanger will overheat, triggering the safety shutdown. That will protect your furnace but leave you in the cold. Fortunately, this is easy to resolve.
Change The Air Filters
Your furnace’s air filter gets clogged with dirt and dust over time, restricting air flow to the furnace. If you have a dirty air filter, all you have to do is change or clean it.
Change a disposable air filter. Replacements are inexpensive and readily available, so stock on a few spares.
Clean a reusable clogged air filter. This type of furnace filter is higher quality, but requires an occasional cleaning. Clean dirty air filters by vacuuming off any dirt and/or gently rinsing and drying according to the manufacturer’s instructions.
Going forward, check the filter monthly, and clean or change your furnace filter at least every 90 days. A clean filter can prevent you from needing to replace or repair your furnace’s heat exchanger.
Open Some Vents
You may have closed a few air vents in the past to block the warm air when your room got too hot. Closed air vents are okay, but make sure some are left open to allow proper airflow to the furnace.
2. Your Thermostat Is The Culprit
Your short cycling furnace could be due to a faulty thermostat. A malfunctioning thermostat may inaccurately read the temperature, causing the furnace to turn on and off unnecessarily.
Check The Setting
Ensure your thermostat is turned on and switched to “HEAT.” Also, double-check the temperature. Someone may have adjusted it to a lower setting than you’d like.
Check Thermostat Communication With The Furnace
Have a buddy stand near the furnace and listen while you adjust the thermostat from “LOW” to “HIGH.” If he or she hears a sound, the problem is probably with your furnace. If not, your thermostat is likely malfunctioning.
Check Thermostat Placement
A thermostat located in a warm spot (for example, it’s close to the kitchen or is frequently in direct sunlight) will register a high temperature and shut the furnace off, while the rest of your room is still chilly.
Talk with us about the best thermostats and the most efficient placement. If your home tends to heat unevenly, or you experience hot and cold spots, consider a heat zoning system.
3. Flame Sensor Is Corroded Or Soot-Covered
A dirty flame sensor is a common issue in gas furnaces and can cause problems such as frequent furnace cycling, failure to ignite, or even a complete shutdown of the heating system. The flame sensor is a safety device that detects the presence of a flame when the burners are on. If it becomes coated with soot or debris, it may not accurately detect the flame.
A dirty flame sensor could be why your furnace keeps shutting off. The flame sensor is a safety device designed to turn off your furnace if no flames are detected, protecting you against dangerous gas fumes. If the flame sensor becomes corroded or covered in soot, it cannot detect flames, even when your furnace is running properly. As a result, the sensor shuts the furnace down.
This is a serious issue requiring prompt professional furnace repair.
4. Oversized Furnace
You may have been sold a furnace which is too large for your home. If your furnace is too big, it will heat your rooms fast. Once the furnace reaches the set temperature, the thermostat will shut it off, causing your house to cool quickly … triggering the furnace to switch on once again. This short cycling pattern won’t provide the home comfort you want, and is hard on your furnace, too.
Alternatively, a furnace that is too small for the heating demands of the space may cycle more frequently as it struggles to maintain the desired temperature.
Look into replacing your under- or over-sized furnace with a new, energy-efficient model that is correctly sized for your needs.
5. Blocked Exhaust Flue
The exhaust flue is responsible for safely venting the combustion gases produced by the furnace to the outside. If the exhaust vent or flue pipe is blocked or restricted, it can lead to a gas valve buildup of these gases, triggering the furnace’s safety mechanism to shut down.
A blocked exhaust flue can pose serious safety risks, including the potential for carbon monoxide buildup. Modern furnaces are equipped with safety features that cause them to shut down when such issues are detected.
Ensure that the exhaust flue is clear of obstructions, such as debris or bird nests. Regular inspections and cleaning are crucial for safe furnace operation and to prevent furnace short cycling.
6. Malfunctioning Blower Motor
The furnace blower fan is responsible for circulating air through the heating system. If the furnace blower motor is malfunctioning, it may not be able to distribute heat effectively. The furnace may then overheat, causing it to shut off as a safety measure.
Inefficient heat distribution, uneven heating, and increased wear on other furnace components can result from a malfunctioning furnace blower motor. Regular maintenance and cleaning of your dirty blower wheel is essential to prevent such issues.
7. High Limit Switch
The fan limit switch is a safety feature designed to shut off the furnace if the temperature inside the system becomes too high. This can happen if there is improper airflow, possibly due to a dirty filter or a malfunctioning blower motor.
Frequent cycling due to a tripped high limit switch can indicate an underlying issue with the furnace, such as poor airflow. Ignoring this issue may lead to more significant problems and reduced furnace efficiency.
Count On Husky For Gas Furnace Repair
When your furnace keeps shutting on and off, it’s a miserable experience. Fortunately, Husky is here, available to service any gas furnace make or model. If you’re in need of furnace replacement or repair, give us a call.
A professional HVAC technician from Husky can perform a more thorough inspection of your heating system, address any underlying issues, and ensure that your furnace operates safely and efficiently. Regular maintenance is essential for the proper functioning of your gas furnace.
Call us 24/7 for emergency services from a professional HVAC technician.
For tune-ups and non-emergency repairs: