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4 common furnace problems and fixes

Men inspecting a furnace
Men inspecting a furnace
Men inspecting a furnace

Tackling furnace issues head on with these tips and techniques

Imagine turning on your furnace on the first cold day of the year to find it’s failing, or worse yet, not working at all. Suddenly you’re stuck in a freezing home until someone can fix it.

Fortunately, scheduling annual maintenance and proactively replacing aging systems can help homeowners prevent most furnace failures. Breakdowns do still occur from time to time, and they can range from inconvenient to downright dangerous.

A carbon monoxide leak is certainly among the most frightening hazards that can originate from a poorly maintained furnace, but it's not the only thing that can go wrong. Here are some of the most common furnace problems and their solutions.

Short cycling

This occurs when a furnace cycles on and off too frequently, often staying on for only a minute or two. There are several potential causes of short cycling, many of which have to do with a furnace's built-in safety systems.

  • If a furnace begins to overheat, which is often caused by restricted airflow (like a clog) through the system, it should automatically shut down to prevent a fire or other heat damage.

  • If it detects a buildup of combustible gases, which can be caused by a clogged flue, it should also be shut down for safety reasons.

  • It may shut down prematurely, if the automatic pilot light ignition is malfunctioning.

  • If your furnace is short cycling, check your air filter to make sure it's not clogged. If you have a gas furnace and can safely access the flue, check it for blockages. If everything appears good, have your furnace inspected by a licensed HVAC technician.

What to do

If your furnace is short cycling, check your air filter to make sure it's not clogged. If you have a gas furnace and can safely access the flue, check it for blockages. If everything appears good, have your furnace inspected by a licensed HVAC technician.

No power to the furnace

If your furnace is completely unresponsive, it may not be receiving any electricity. 

What to do

Carefully examine your furnace to ensure that it hasn't become physically disconnected from its power source (if it connects to an outlet). You should also check for a shut-off switch or button to make sure it wasn't inadvertently activated.

Furnaces draw a lot of power and may also trip a circuit breaker. Check your electrical panel to see if your furnace's circuit breaker is tripped. If it is, flip it back to the "on" position. If it trips again, call an HVAC technician or electrician to assess the problem because this usually indicates some sort of malfunction.

Pilot light problems

Some older natural gas furnaces have a pilot light – a small flame that burns continuously. Any sort of strong airflow could potentially blow the pilot light out. It could also go out due to dust buildup, a failed thermocouple, or other causes. 

What to do

If your pilot light goes out, you can attempt to re-light it yourself. Start by clearing the area of any natural gas fumes that may have accumulated before following your furnace's manufacturer instructions.

Newer gas furnaces use an electronic ignition instead of a pilot light, but these parts can also fail over time or simply become clogged up with dust or dirt. No matter which type of ignition your furnace has, you should call in a professional if you suspect that your pilot light or igniter is repeatedly failing.

Loud noises

A loud scraping or grinding noise when you operate your furnace is usually a sign of fan problems caused by worn out ball bearings, bent fan blades, or alignment issues. If you hear more of a squealing or squeaking sound, this typically indicates a worn drive belt somewhere in the system. A worn drive belt will eventually break, bringing your HVAC system to a halt.

What to do

If it’s a fan problem, have a licensed professional inspect these parts of your furnace and replace or lubricate them as needed to quiet things down again. Belt problems require replacement by a professional as soon as possible. 

Be proactive about furnace care

Taking care of your furnace is relatively simple; change the air filters as suggested by the manufacturer (usually every one to three months), and have your furnace professionally tuned up once a year. If you have worn parts that need replacing, your annual tune-up is a great opportunity to catch and address these issues before they lead to a breakdown.

Want to hear a real furnace horror story? Gather ‘round the pilot light for this episode of This American Life.

To avoid a furnace nightmare of your own, consider a Protection Plan to help you cover unexpected furnace costs and stay on top of maintenance.


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