Furnace Repair Brampton

Reasons a Furnace Keeps Shutting Off When It Ignites

furnace keeps shutting off when it ignites

It can be quite a nerve-wracking experience to have your furnace shutting off while it’s ignited. Not only could you use more energy as the heating cycle restarts multiple times, but you may also worry about safety and potential risks associated with continuous on-and-off cycling of your furnace.

To help put your mind at ease, we want to provide an in-depth look into why furnaces keep shutting off when they ignite so that you can consider what steps might be necessary for proper repair or maintenance. Keep reading to learn more about critical factors that cause a furnace motor to continuously turn on and off!

Lack of Maintenance

Lack of maintenance is one of the most common reasons a furnace keeps shutting off when it ignites. Regular furnace maintenance is crucial to keep your system running smoothly and to prevent potential problems.

A lack of maintenance can cause various furnace issues, including a lack of proper airflow, which can cause the furnace to shut off when it ignites. Some of the ways lack of maintenance can impact your furnace include the following:

Dirty Furnace Filter: A dirty furnace filter can restrict airflow, leading to overheating and potentially causing the furnace to shut off. Regular filter replacement and cleaning can help prevent this issue.

Clogged Burners: Dirt and debris can accumulate on the furnace burners, leading to clogs that restrict airflow and cause the furnace to shut off. Annual cleaning by a licensed HVAC technician can prevent this issue.

Ignition Problems: Ignition problems can result from a lack of maintenance, including debris buildup around the ignition components. It can cause the furnace to shut off when it ignites, and regular cleaning can help prevent these problems.

Prevention Tips

You can follow several prevention tips to keep your furnace running smoothly and avoid issues related to lack of maintenance. These include:

  • Schedule Regular Maintenance: Schedule annual maintenance by a licensed HVAC technician to keep your furnace in top condition.
  • Replace Filters Regularly: Replace your furnace filter every three months or more frequently if you have pets or live in a dusty environment.
  • Keep the area around the Furnace Clean: Keep the area around your furnace clean and free of debris to ensure proper airflow and reduce the risk of clogs.

Faulty Thermostat

A thermostat is responsible for controlling your home’s temperature, and if it is malfunctioning, it can cause the furnace to turn off when it ignites. The thermostat uses sensors to detect temperature changes and signals the furnace to turn on and off accordingly. A faulty thermostat can cause various problems, including:

  • Inaccurate Temperature Readings: If the thermostat is not accurately reading the temperature, it may signal the furnace to turn off prematurely, even if the desired temperature has not yet been reached.
  • Short Cycling: Short cycling occurs when the furnace turns on and off frequently, putting a strain on the system and causing it to shut off when it ignites. A faulty thermostat can cause this issue.
  • Electrical Problems: A faulty thermostat may short-circuit or have other electrical problems, leading to the furnace shutting off when it ignites.

Symptoms of a Faulty Thermostat

If you suspect that your thermostat is the problem, there are several symptoms to look out for, including:

  • If the temperature reading on your thermostat seems off or does not match the actual temperature in your home, it may be a sign that your thermostat is faulty.
  • Frequent on-and-off cycling of your furnace indicates that something is not functioning correctly in your HVAC system, and your thermostat may be to blame.
  • If your furnace is not turning on, it may result from a faulty thermostat.

Dirty Flame Sensor

The flame sensor is an essential component of your furnace’s ignition system. It detects the flame, signals to the furnace that it is safe to continue operating, and keeps the gas valve open. The importance of a clean flame sensor cannot be overstated, as a dirty or malfunctioning sensor can cause the furnace to shut off when it ignites. Regular cleaning can help ensure your flame sensor functions correctly and keep your furnace running smoothly.

A dirty flame sensor can fail to detect the flame correctly, leading to the furnace shutting off. Several things can cause buildup and dirt on the flame sensor, including:

Dust and Dirt: Dust and dirt in the furnace system can accumulate on the flame sensor, causing buildup that interferes with the sensor’s ability to detect the flame correctly.

Rust: Rust in the furnace system can corrode the flame sensor, causing it to malfunction and fail to detect the flame correctly.

Aging Components: As the furnace and its components age, they can accumulate dirt and debris, leading to a dirty flame sensor that causes the furnace to shut off when it ignites.

Clogged Air Filter

The air filter in your furnace plays a vital role in maintaining its efficiency and performance. The primary purpose of the air filter is to remove dust, dirt, pollen, and other airborne contaminants from the air entering your home. It also helps maintain system pressure balance, ensuring that there is enough air flowing through your system for it to run efficiently. Without a clean air filter, these particles will circulate throughout your home’s ducts and into the living spaces of your home.

A dirty or clogged air filter can reduce airflow to your furnace, causing it to shut off when it attempts to ignite due to insufficient airflow. This reduced airflow can also increase energy usage as the system must work harder to push heated or cooled air through clogged filters. Additionally, a dirty air filter can introduce additional stress on other components in the system, such as blowers and heat exchangers, which may result in premature failure of these parts.

It is recommended that you replace your furnace’s air filter every 1-3 months, depending on the type of filter used and how much debris it has been exposed to. If you live in an area with high levels of dust or pollen present in the environment, then more frequent replacements may be necessary for optimal performance. Replacing your furnace’s air filters regularly is an easy way to keep your system running smoothly and help ensure maximum efficiency!

Malfunctioning Gas Valve

The gas valve is an essential component of your furnace’s ignition system, as it controls the fuel flow from the main supply line to the burners in your furnace. It is also responsible for monitoring and regulating fuel pressure, ensuring enough fuel is supplied to maintain proper operation. Without a properly functioning gas valve, your furnace may not ignite or may shut off when it does ignite.

A malfunctioning gas valve can cause several issues with your furnace, including:

Insufficient Fuel Pressure: If the pressure of the fuel entering your furnace is insufficient due to a faulty or corroded valve, the burners may not be able to provide enough heat and may shut off prematurely when ignited.

Air Leaks: A faulty valve can allow air into the fuel lines due to worn seals and gaskets, leading to inefficient combustion and premature shutdowns when ignited.

Malfunctioning Control Panel: If the control panel on your furnace cannot detect that there is sufficient pressure in your fuel lines due to a faulty gas


If your furnace keeps shutting off when it ignites, several causes exist. These include dust and dirt buildup on the flame sensor, a dirty or clogged air filter reducing airflow to the furnace, and a malfunctioning gas valve. It is recommended that an HVAC professional inspect your furnace to determine what is causing the issue and develop a repair plan. Regular furnace maintenance is also essential to ensure that your furnace operates efficiently and reliably in the winter.