Furnace Stopped Working: Top 10 Reasons

A furnace breakdown is a major inconvenience, especially during the colder months when you rely on it the most. Understanding the reasons behind these malfunctions can help you stay prepared and possibly prevent a total shutdown.

In this article, we’ll explore the most common reasons your furnace stopped working, provide insights on potential issues, and offer solutions on how to tackle them or when to call a professional.

10 common reasons your furnace stopped working

1. Lack of power supply

If your furnace has suddenly stopped working, the first thing to check is whether it is receiving power. Ensure that the circuit breaker or fuse for the furnace is in the “on” position. If it has tripped or blown, reset the breaker or replace the fuse. If the power supply seems fine, you can move on to other possible causes.

2. Thermostat issues

A malfunctioning thermostat can prevent your furnace from turning on. Check if the thermostat display is blank or if the temperature setting is incorrect. Replace the batteries if applicable and ensure that the thermostat is set to “heat” mode. If these steps don’t work, you may need to replace the thermostat.

3. Clogged air filter

A clogged air filter can restrict airflow and cause the furnace to shut off. Inspect the air filter and replace it if it appears dirty or clogged. Regularly changing the air filter every three months can help prevent this issue.

4. Pilot light problems

For older gas furnaces, a common reason for malfunctioning is a pilot light that has gone out. Follow the manufacturer’s instructions to safely relight the pilot light. If the pilot light keeps going out or won’t stay lit, it could indicate a more significant issue that requires professional assistance.

5. Ignition system failure

Modern furnaces often use electronic ignition systems that might fail over time. If your furnace has intermittent or no ignition at all, it may be due to a faulty ignition system component. Contact a qualified technician to diagnose and repair this issue.

6. Blower motor failure

If you notice that the furnace’s blower motor isn’t running, it could be due to a faulty motor or a problem with its capacitor. In such cases, it’s best to consult with a professional HVAC technician who can properly diagnose and repair the motor or capacitor.

7. Gas supply issues

Gas furnaces require a steady supply of gas to operate correctly. If there’s an issue with the gas supply, such as a closed valve or low gas pressure, it can cause the furnace to stop working. Check if other gas appliances are functioning correctly, and if not, contact your gas utility company for assistance.

8. Faulty limit switch

The limit switch is a safety feature that detects when the furnace gets too hot and shuts it down to prevent damage. If the limit switch is faulty, it may cause the furnace to stop working prematurely. This issue usually requires professional attention to replace the faulty switch.

9. Blocked vents or ducts

Blocked vents or ducts can restrict airflow and cause issues with your furnace’s performance. Check for any obstructions, such as furniture, rugs, or debris blocking the vents, and clear them away. Additionally, ensure that all vents and ducts are clean and free from dirt or dust buildup.

10. Overload protection activation

In some cases, the furnace’s overload protection may have been triggered due to an electrical overload or short circuit. Locate the overload switch (usually near the blower motor) and reset it by turning it off and then back on again. If this continues to occur, consult a professional for further inspection and repairs.

Can a thermostat failure cause a furnace to stop working?

Yes, a thermostat failure can cause a furnace to stop working. The thermostat is responsible for signaling the furnace to turn on and off based on the desired temperature settings.

If the thermostat malfunctions, it may not send the correct signals to the furnace, resulting in it not turning on at all. This can be due to a blank display, incorrect temperature readings, or issues with the thermostat’s internal components.

In such cases, replacing the batteries, checking the settings, or replacing the thermostat itself might be necessary to restore proper functionality to the furnace.

How do I restart my furnace?

Check the power supply. Ensure that the circuit breaker or fuse for the furnace is in the “on” position. If it has tripped or blown, reset the breaker or replace the fuse.
Reset the thermostat: Turn off the thermostat and wait for a few minutes. Then, set it to the desired temperature and switch it to “heat” mode.
Check the pilot light (for gas furnaces): If you have an older gas furnace, make sure the pilot light is lit. Follow the manufacturer’s instructions to relight it safely if necessary.

Inspect the air filter. Check if the air filter is dirty or clogged. Replace it if needed, as a clogged filter can affect the furnace’s performance.
Verify the vents and ducts: Ensure that all vents and ducts are free from obstructions such as furniture or debris. Clear any blockages that may impede airflow.
Turn on the furnace: Locate the power switch on your furnace and set it to the “on” position. Give it a few moments to start up and begin heating.

Is it possible to fix a broken furnace on my own?

While there are certain furnace issues that homeowners can address on their own, such as replacing an air filter or checking the thermostat settings, attempting to fix a broken furnace without proper knowledge and experience can be risky.

Furnaces involve complex systems, electrical components, and potentially hazardous gases (in the case of gas furnaces). Incorrect repairs or troubleshooting may lead to further damage or safety hazards.

It is always recommended to contact a qualified HVAC technician for furnace repairs. They have the expertise, tools, and understanding of safety protocols to diagnose and fix the issue correctly, ensuring the long-term reliability and safety of your furnace.

What are the signs of a failing furnace?

Insufficient heating: If your furnace is not providing enough heat or the temperature in your home is consistently lower than the desired setting, it could indicate a problem with your furnace.
Strange noises: Unusual sounds such as banging, grinding, rattling, or squealing coming from your furnace may suggest mechanical issues or loose components that require attention.
Frequent cycling: If your furnace turns on and off frequently, known as short cycling, it could be a sign of an underlying problem such as a malfunctioning thermostat, a clogged air filter, or improper airflow.

Increased energy bills: A sudden spike in your energy bills without any significant changes in usage could indicate reduced efficiency or a malfunctioning component within your furnace.
Uneven heating: If certain areas of your home are significantly colder than others, it may indicate airflow problems, duct issues, or malfunctioning components in the furnace.
Yellow burner flame: A yellow or flickering flame instead of a steady blue flame in a gas furnace can indicate incomplete combustion, potentially due to a problem with the burner or gas supply.

Constant repairs: If you find yourself frequently needing to repair your furnace or if the same issues keep recurring, it may be a sign of a failing system that requires replacement.

How can regular furnace maintenance prevent unexpected failures?

By scheduling routine maintenance, a qualified HVAC technician can inspect and clean your furnace, identify potential issues early on, and address them before they escalate into major problems.

Regular maintenance includes tasks such as cleaning or replacing air filters, checking and adjusting thermostat settings, lubricating moving parts, inspecting electrical connections, cleaning the blower motor and fan blades, and verifying gas or fuel supply.

This proactive approach helps optimize the furnace’s performance, improve energy efficiency, extend its lifespan, and minimize the risk of unexpected breakdowns during critical times, providing you with peace of mind and a comfortable living environment.

What professional services are available for furnace repair?

There are various professional services available for furnace repair. HVAC companies and technicians specialize in diagnosing and fixing issues with furnaces.

They have the expertise, experience, and necessary tools to handle a wide range of furnace problems, from simple repairs to complex system troubleshooting. These professionals can identify faulty components, perform repairs or replacements, clean and maintain the furnace, and ensure it is operating safely and efficiently.

If you are looking for a reliable contractor for furnace repair or any other home improvement project, you can explore our contractor directory called Big Home Projects, which provides a listing of trusted contractors in your area.

When should I consider replacing rather than repairing a furnace?

Age of the furnace: If your furnace is approaching or has exceeded its expected lifespan (typically around 15–20 years), it may be more cost-effective to replace it rather than invest in frequent repairs.
Frequency and cost of repairs: If your furnace requires frequent repairs or if the repair costs are becoming significant, it may be more economical to replace the unit. As a general rule, if the repair cost exceeds 50% of the cost of a new furnace, replacement is often recommended.

Energy efficiency: Older furnaces tend to be less energy-efficient compared to newer models. If your furnace has a low AFUE (Annual Fuel Utilization Efficiency) rating and is causing high energy bills, upgrading to a newer, more efficient model can help save on energy costs in the long run.
Uneven heating or comfort issues: If your furnace is struggling to heat your home evenly or if you’re experiencing comfort issues, even after repairs, it may be a sign that the furnace is no longer capable of meeting your heating needs effectively.
Safety concerns: If your furnace poses safety risks due to frequent malfunctions, carbon monoxide leaks, or other hazardous issues that cannot be adequately resolved through repairs, it is crucial to prioritize your safety and consider replacing the furnace.