What Could Go Wrong with My Furnace?

There's almost no such thing as a small furnace problem. If your furnace isn't keeping up or isn't working at all, you're left with a freezing home – which is more than a minor inconvenience. And as one of the most energy-hungry appliances in your home, if your furnace is running inefficiently, it can make a huge impact on your wintertime energy bills. So when something goes wrong with this critical system, the repair professionals can't arrive soon enough.

Fortunately, scheduling annual maintenance and proactively replacing aging systems is all the typical homeowner has to do to prevent most catastrophic furnace failures. But breakdowns do still occur from time to time, and some of them can be downright scary.

One such story was published in the "American Journal of Opthalmalogy" back in 1921 (and recounted by "This American Life" in 2006), via a letter from a patient to her doctor. The letter described a strange and unsettling series of events that followed his family's relocation to a large, gloomy mansion:

"One morning, I heard footsteps in the room over my head. I hurried up the stairs. To my surprise, the room was empty. I passed into the next room, and then into all the rooms on that floor, and then to the floor above, to find that I was the only person in that part of the house.

Sometimes after I've gone to bed, the noises from the store room are tremendous, as if furniture was being piled against the door, as if china was being moved about, and occasionally, a long and fearful sigh or a wail. Sometimes as I walk along the hall, I feel as if someone was following me, going to touch me. You cannot understand it if you've not experienced it. But it's real.

As I was dressing for breakfast one morning, B, who is four years old, came to my room and asked me why I'd called him. I told him I had not called him, that I had not been in his room. With big and startled eyes, he said, 'Who was it then that called me? Who made that pounding noise?' I told him it was undoubtedly the wind rattling his window. 'No,' he said, 'It was not that. It was somebody that called me. Who was it?' And so on he talked, insisting that he'd been called and for me to explain who it had been."

But this was no supernatural event. The home's dilapidated furnace, as well as its network of gas lights, was leaking carbon monoxide into the home, causing hallucinations. As soon as the leaks were discovered and repaired, the family's terrifying experiences stopped.

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

When a furnace cycles on and off too frequently, often staying on for only a minute or two, it's a problem HVAC professionals call "short cycling." 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 can be caused by restricted airflow through the system, it should automatically shut down to prevent a fire or other heat damage. If it detects a buildup of combustible gasses, which can be caused by a clogged flue, it should also shut down for safety reasons. It may even 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. A dirty air filter may restrict airflow to the extent that it overheats a furnace. If you have a gas furnace and can safely access the flue, check to ensure that there aren't any blockages. If everything looks good, have your furnace inspected by a licensed HVAC technician, who can help pinpoint the source of the problem and make necessary repairs.

No Power to the Furnace

If your furnace is completely unresponsive, one of the possible causes is that it's not receiving any electricity. Furnaces are usually hardwired for electricity, but in some installations, they may have a corded plug that connects to an outlet. Carefully examine your furnace to ensure that it hasn't become physically disconnected from its power source. You should also check for a shut-off switch or button to make sure this 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, and 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 repeated circuit breaker trips usually indicate some sort of malfunction.

Pilot Light Problems

Some older natural gas furnaces have a pilot light – a small flame that is designed to burn continuously to provide an ignition source for the burner. Any sort of strong airflow in the area of your furnace could potentially blow the pilot light out, and it could also go out due to dust buildup, a failed thermocouple or any of several other causes. If your pilot light goes out, you can attempt to re-light it yourself by following your furnace's manufacturer instructions, but you must take care to first clear the area of any natural gas fumes that may have accumulated.

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 – perhaps the ball bearings have worn out, or maybe your fan has bent blades or has fallen out of alignment. A licensed professional can inspect these parts and replace and/or lubricate them as needed to quiet things down again.

If you hear a squealing or squeaking sound, this typically indicates a worn drive belt somewhere in the system. You should have this replaced by a professional as soon as possible, because a worn drive belt will eventually break, bringing your HVAC system to a halt.

Be Proactive About Furnace Care

As they say, an ounce of prevention is worth a pound of cure. Taking care of your furnace is relatively simple; change the air filters per the filter manufacturer's suggested intervals (usually every month or every three months) and have your furnace professionally tuned up once per 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.

You can find more tips for taking care of your home in our Learning Center.

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