10 Common Reasons Your Furnace Won’t Turn On and How to Fix Them

Is your furnace refusing to turn on, leaving you in a chilly predicament? Understanding the potential causes of this frustration can empower you to troubleshoot and possibly rectify the issue before reaching out to a professional.

In this article, we will delve into the ten common reasons your furnace might not be turning on, along with a helpful guide to fixing each problem.

10 reasons your furnace won’t turn on and how to fix them

1. Thermostat malfunction

If your furnace won’t turn on, the first thing to check is the thermostat. Ensure that it is set to the desired temperature and in the “heat” mode. If the display is blank, check the batteries or power supply. If the thermostat is programmable, double-check that the schedule is correctly set. If necessary, replace the batteries or reset the thermostat.

2. Tripped circuit breaker

A tripped circuit breaker can prevent your furnace from turning on. Check the circuit breaker panel and locate the one labeled for the furnace or HVAC system. If it has tripped, reset it by flipping it to the “off” position and then back to the “on” position. If the breaker trips again, there may be an electrical issue that requires professional assistance.

3. Clogged air filter

A clogged air filter restricts airflow and can cause your furnace to malfunction. Locate the air filter, which is usually found near the blower motor or in a return air grille. Remove the filter and inspect it for dirt and debris. If it appears dirty or clogged, replace it with a new one of the same size and type. Regularly replacing air filters every 1-3 months is essential for proper furnace operation.

4. Lack of power supply

Ensure that your furnace is receiving power. Check if the power switch near the unit is turned on. If it was off, turn it on and see if the furnace starts running. Also, inspect the electrical panel to see if a fuse has blown or a breaker has tripped. Replace any blown fuses and reset tripped breakers. If these steps don’t restore power, contact a qualified HVAC technician.

5. Gas supply issues

If you have a gas furnace, make sure it has a sufficient supply of gas. Check other gas appliances in your home to ensure they are functioning properly. If they are not, contact your gas utility company to investigate any potential gas supply issues. If the gas supply seems fine but the furnace still won’t turn on, it’s advisable to call a professional technician to inspect the system.

6. Ignition problems

Furnaces with electronic ignition systems may experience ignition problems, preventing them from starting. If you hear a clicking sound but the furnace doesn’t ignite, there might be an issue with the ignition system. In some cases, simply cleaning the ignition sensor or thermocouple can solve the problem. However, it is recommended to have a professional technician diagnose and repair any ignition-related issues.

7. A faulty blower motor

A faulty blower motor can cause your furnace not to turn on. If you don’t hear the familiar sound of the blower motor running, it may need attention. Check for any loose or damaged wiring connections. If no visible issues are found, it’s best to contact an HVAC technician to inspect and repair the blower motor, as it requires specialized knowledge and tools.

8. Blocked ventilation system

Obstructions in the ventilation system can prevent proper airflow and cause your furnace to shut down for safety reasons. Check the vents and ducts for blockages caused by debris, ice, or even small animals. Clear away any obstructions and ensure that all vents are open and unobstructed. This should allow for adequate airflow and help your furnace function properly.

9. Flame sensor problems

For gas furnaces, a malfunctioning flame sensor can prevent ignition. The flame sensor is a safety feature that detects whether a flame is present and shuts off the gas valve if no flame is detected. Over time, the sensor can become dirty or develop corrosion, causing it to malfunction. Cleaning the flame sensor with fine-grit sandpaper or contacting a professional for maintenance can resolve this issue.

10. Faulty control board

If all else fails, a faulty control board might be the culprit behind your furnace not turning on. The control board is the brain of the furnace, responsible for coordinating various functions. If it becomes damaged or malfunctions, it can prevent the furnace from operating correctly. In this case, it’s best to consult with an HVAC technician to diagnose and replace the faulty control board if necessary.

Is there a power supply issue causing my furnace not to turn on?

If your furnace is not turning on, a power supply issue could be one of the potential causes.

To determine if there is a power supply problem, start by checking if the power switch near the furnace unit is turned on.

Inspect your electrical panel to see if a fuse related to the furnace has blown or if a breaker has tripped. If you find a blown fuse, replace it with a new one of the same rating.

For a tripped breaker, flip it to the “off” position and then back to “on”.

Could my furnace’s thermostat be causing the issue?

A malfunctioning thermostat can be a potential cause of your furnace not turning on. Start by checking the thermostat settings to ensure it is set to the desired temperature and in “heat” mode.

If the thermostat display is blank, check the batteries or power supply. If it is a programmable thermostat, double-check that the schedule is correctly set. If needed, replace the batteries or reset the thermostat.

Dust or debris accumulation around the thermostat can interfere with its functionality, so gently clean around it.

What role does ignition play when my furnace does not turn on?

The ignition system plays a crucial role in starting your furnace. When your furnace does not turn on, ignition problems could be a potential cause. Furnaces with electronic ignition systems typically produce a clicking sound during the startup process.

If you hear the clicking sound but the furnace fails to ignite, it indicates an issue with the ignition system. This could be due to a dirty or malfunctioning ignition sensor or thermocouple. Cleaning these components with fine-grit sandpaper might resolve the problem.

However, have a professional technician diagnose and repair any ignition-related issues, as they require specialized knowledge and tools to ensure proper functioning and safety.

How does a dirty air filter affect the furnace’s operation?

A dirty air filter can significantly impact the operation of your furnace. When the air filter becomes clogged with dirt, dust, and debris, it restricts the airflow passing through the system.

As a result, the furnace has to work harder to draw in air, which can lead to various issues.

Restricted airflow can cause the furnace to overheat, triggering safety mechanisms that shut down the system to prevent damage.

Reduced airflow affects the efficiency of heat exchange, leading to decreased heating performance and a potentially uneven distribution of heated air throughout your home.

A clogged air filter can strain the blower motor, increasing energy consumption and potentially causing premature wear and tear. Regularly replacing or cleaning the air filter is crucial to maintaining optimal airflow and ensuring the proper functioning and longevity of your furnace.

A step-by-step guide to troubleshooting a non-functioning furnace

Check the thermostat: Ensure that the thermostat is set to the desired temperature and in “heat” mode. If the display is blank, check the batteries or power supply. Clean around the thermostat if there is any dust or debris.
Inspect the power supply. Verify that the power switch near the furnace unit is turned on. Check the electrical panel for any blown fuses or tripped breakers related to the furnace. Replace blown fuses and reset tripped breakers.
Examine the air filter: Locate the air filter and inspect it for dirt and debris. If it appears dirty or clogged, replace it with a new one of the same size and type. Clean or replace air filters regularly to ensure proper airflow.

Ensure gas supply (for gas furnaces): Check other gas appliances in your home to ensure they are functioning properly. If they are not, contact your gas utility company to investigate any potential gas supply issues.
Check the ventilation system: Inspect vents and ducts for obstructions caused by debris, ice, or animals. Clear away any blockages and ensure vents are open and unobstructed to allow proper airflow.
Inspect the ignition system (for electronic ignition): Listen for a clicking sound when the furnace starts up. If you hear clicking but no ignition, clean the ignition sensor or thermocouple using fine-grit sandpaper. If the issue persists, contact a professional technician.

Verify the blower motor: Listen for the sound of the blower motor running. Check for loose or damaged wiring connections. If no visible issues are found, seek assistance from an HVAC technician to diagnose and repair the blower motor.
Clean flame sensor (for gas furnaces): If you have a gas furnace and it fails to ignite, a dirty or corroded flame sensor might be the problem. Clean the flame sensor with fine-grit sandpaper or seek professional maintenance.
Check the control board. If all else fails, a faulty control board could be the cause. Consult an HVAC technician to diagnose and replace the control board if necessary.

When to seek professional help for a furnace not turning on

In several situations, it is advisable to seek professional help if your furnace is not turning on.

If you have already attempted basic troubleshooting steps without success,
If you are uncomfortable with or lack experience dealing with electrical components, gas systems, or complex HVAC repairs.

If you notice any signs of gas leaks, unusual odors, or other safety concerns,
If you suspect a more significant underlying issue, such as a faulty control board or blower motor,
If your furnace is still under warranty, attempting repairs yourself could void the warranty.

In these cases, it is best to contact a qualified HVAC technician. You can find professional HVAC technicians and contractors on the Big Home Projects directory site who can assist you in diagnosing and resolving the issue with your furnace.

How regular maintenance influences furnace performance

Regular maintenance plays a crucial role in maintaining the performance and efficiency of your furnace. By scheduling routine maintenance, such as annual inspections and tune-ups, you can ensure that your furnace operates at its best.

During maintenance, HVAC professionals clean and inspect various components, including the burners, heat exchanger, blower motor, and electrical connections.

They also check for any signs of wear or potential issues that could affect performance or lead to breakdowns. Maintenance allows for the timely replacement of worn-out parts, optimizing energy efficiency, and preventing costly repairs.

Regular maintenance helps extend the lifespan of your furnace, improves its reliability, enhances indoor comfort, and can even contribute to lower energy bills.

What is the basic function of a furnace?

A furnace is a heating system that works by generating and distributing warm air throughout a building. The basic functioning of a furnace involves several key components.

The process typically begins with the thermostat, which detects the desired temperature and signals the furnace to start. The burner ignites a mixture of fuel, commonly gas or oil, within the combustion chamber.

As the fuel burns, heat is produced and transferred to the heat exchanger. The blower motor then circulates the heated air through the ductwork and vents after the heat exchanger has warmed it up, distributing it into various rooms.

Meanwhile, combustion byproducts are safely vented outside through a flue or chimney. This cycle continues until the desired temperature is reached, at which point the furnace shuts off until the thermostat signals it to start again.