The furnace is the unsung hero of winter, soldiering on to keep us warm and toasty during the most frigid months of the year. However, we give little thought to this essential household item, unless it becomes temperamental or stops working altogether. When your furnace goes out in the dead of winter, do you know what to do? Is it an easy fix? Should you call a professional? 

Here’s what you need to know before the temperature dips too low.


Clogged air filter

Your furnace has an air filter that traps dust and debris. When the filter is clogged, your furnace has to work harder. Dirty filters cause short cycling times. The lack of fresh air into your furnace causes the heat exchanger to get too hot, and shut down, which makes it hard for your home to stay warm. A furnace that doesn’t produce enough heat typically is due to an air filter problem. Plus, dirty filters hurt the air quality in your home. If you don’t keep up with air filter replacements, it could lead to a costly expense—that of a cracked heat exchanger. To prevent issues, change your filters regularly as part of your seasonal maintenance. For paper filters, change them every 3-6 months. For fiberglass filters, change them every 2 months. 

The quick fix: Change your air filter. You can tell that it’s time to do so if you hold it up to the light, and no light shines through. Make sure to insert the new filter correctly. Air filters are made to trap debris blown from one direction. Installing a filter upside-down can limit its effectiveness.

When to call a professional: If you have electrostatic filters, they can last for years if cleaned regularly. Ask your furnace professional how to change these filters. Finally, if you do have a cracked heat exchanger, that requires a professional. 


Blower issues

Furnaces that are not blowing air or those that are continually blowing air are both a problem. If your furnace is not blowing air, it could be clogged. Or it’s possible that the access door to the furnace door is off or unhinged. The safety switch on the door prevents the fan and burner from coming on unless the door is shut. Alternately, if the blower continually runs, the heat rises, which means the limit switch isn’t doing its job. It’s supposed to shut down the blower when the temperature inside the furnace becomes dangerously hot. A bad limit switch will significantly shorten the lifespan of your furnace blower.

The quick fix: For furnaces that are not blowing air, you can clean your blower fan. This requires removing the blower from the furnace. Call a technician if you haven’t done this before or if the red light is flashing on your unit, signaling a problem.

When to call a professional: A bad limit switch needs to be replaced. This has to be done by a professional.


Malfunctioning thermostat

The thermostat is the control center of your home heating system. When it’s not working properly, your furnace won’t function at its best either. It could be cycling on and off more than usual or fail to produce enough heat. The fan could be running constantly. This drains the battery and causes your furnace to work inefficiently. 

The quick fix: For electronic thermostats, try replacing your thermostat’s batteries. For manual thermostats, take off the thermostat cover and dust the inside with a small brush. Look for a tripped circuit breaker and reset it, or a blown fuse and replace it. Set the fan on auto and see if your furnace runs constantly through all heat settings.

When to call a professional: If your wires are connected but the thermostat isn’t working properly, call an expert. He/she will be able to test the wires individually to determine which is faulty.


Pilot light/electric ignition

Your gas furnace has a pilot light, which ignites the natural gas pumped into the main burner. Your electric furnace has an electric ignition, which performs a similar function. If these are not working properly, you could have problems getting heat. A gas pilot light should be blue; that indicates it’s burning properly with enough oxygen. If it’s flickering yellow, that could be a sign of excess carbon monoxide or dirt built up on the intake valve, preventing oxygen from feeding the flame. 

The quick fix: If it’s a gas pilot and it’s simply gone out, try relighting. It. If it’s an electric ignition, check to make sure it’s not a tripped breaker causing the problem. You can also try turning off your furnace’s supply of power, wait for 10 minutes, and turn it back on.

When to call a professional: If you relight the gas pilot and it keeps going out, call a professional. If the pilot is yellow or orange, that also warrants a professional look. It could be caused by an old igniter or a faulty temperature limiting switch.


Rumbling, squeaking, and rattling noises

If your furnace is making noises, chances are something is wrong. A high-pitched squeal could be a frayed or slipped blower belt, which helps your furnace fan run. Worn-out ball bearings could cause a scraping sound. If your furnace makes a loud sound when you start it up, that could mean there’s oil buildup in the chamber and it’s ignited all at once. Rattling could be caused by a loose duct. Whistling could be caused by a clogged air filter.

The quick fix: If you hear whistling, try replacing the air filter. If your furnace is rattling or vibrating, make sure loose ducts are screwed down properly. You can also try to add some pads under the furnace to level it.

When to call a professional: If you hear a scraping sound, turn the furnace off immediately and call a professional. Do the same if there’s a loud sound upon starting up the furnace. It’s a good idea to get sounds checked out to prevent future problems and potentially dangerous situations.


Leaking water

Standard furnaces don’t produce water but high-efficiency models do. There are several causes for a furnace leaking water, including a clogged condensation tube or drain hose. Loose connections, cracks, and holes can also cause water to leak. Condensate pumps typically last for 3-5 years; they can also start malfunctioning after that time.

The quick fix: Turn off the system either by the switch on the unit or the breaker. Clean up the water from around the base. You can use a wet-dry vacuum if needed to unclog the condensate drain line. 

When to call a professional: You will need a professional to replace your condensate pump and any other parts.


Safety first

Keep in mind that do-it-yourself furnace repair does present some potential safety issues, from fire and other winter home hazards to carbon monoxide poisoning. Small repairs done improperly can lead to bigger issues, and you might void the warranty on the appliance if you accidentally cause a larger problem. Unless you received training in furnace repair, limit your fixes to the simple ones. Leave any mechanical repairs to the professionals.

Homeowner’s insurance covers repairs or replacement of furnaces if they are damaged by a covered condition on your policy, such as water damage from a burst pipe. Check with your policy provider to find out more.


This article is furnished by California Casualty, providing auto and home insurance to educators, law enforcement officers, firefighters, and nurses. Get a quote at 1.866.704.8614 or

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