Furnace Problems – Top Causes

Those of us in northern climes know all too well that it’s impossible to live without a furnace in the winter. If you’ve ever had furnace problems during freezing weather, you know that a warm house is far preferable to wrapping yourself in layers of blankets and drinking hot tea to ward off the chill.

A furnace is a mechanical system, and, like any other system composed of multiple parts, things can go wrong. Luckily, they’re treatable, and your HVAC professional will be happy to assist you in fixing anything that is a technical challenge. That’s their calling. First, however, you can try to narrow down the problem by learning a bit more about the usual reasons for heating problems.

The Thermostat.

Before you head to the basement to start unscrewing things, take a look at the part of the heating system that might be right in front of you: the thermostat. It sounds obvious, but checking that thermostat before making a phone call could save many homeowners time and money. If you have it set to “OFF” or to “COOL,” it’s pretty clear that you won’t be getting any heat in the house. If it’s set to “HEAT,” but at a temperature lower than the current room temperature, it won’t kick on until you adjust the setting. If your thermostat is battery operated, you may also want to check the batteries. It’s worth changing them every few months to avoid a crisis during the winter.

Breakers and Switches.

Another obvious place to look is at the power that keeps the furnace running. If you don’t have it switched on or if there is a blown fuse, it could be causing your furnace to malfunction. If everything is just a bit too quiet – no fan motor running or no sound of the furnace kicking into gear – you’ll want to check the breakers and switches that ensure there’s power available to your furnace.


Is your furnace shutting down before the house is warm? If so, you may have a filter coated with layers of dust and dirt that is preventing the air from flowing properly. Furnace filters are the barriers that keep dust and allergens from spreading throughout your home, but they need to be changed regularly so they can do their job properly. Dirty filters can even cause problems with the furnace itself over time. Changing filters every three months is a good rule of thumb.

Gas/Pilot Light.

If your furnace is on the blink, you might be the victim of ignition failure. Be certain that the gas valve is open so there is fuel going to your furnace, and make certain that if your model has a pilot light, it is lit. Open the door to the burner chamber and check to see if there is a flame burning. If not, you’ll need to light it; it’s similar to a gas stove in that regard.

Blocked Vents.

Is your bookshelf standing right in front of the air vent in your office? If you hear the air go on but aren’t feeling the “burn,” an air register or vent may be blocked or closed. Anything obstructing a vent can cause your furnace to work harder than necessary to heat the space or cause it to overheat, so it’s time to “clear the air.”

Motor Malfunction.

If the blower or fan motor isn’t working, the furnace can generate all the heat in the world, but it won’t move through your home. This is a problem for an HVAC professional, so don’t try to fix it yourself.

Clogged Drain Lines.

Boilers and high-efficiency furnaces each have drain lines to carry away condensation, so be sure there is no mould or sediment in the lines or hose that could cause them to become plugged. If you can flush them, you’ll get more efficiency from your furnace or boiler.

Intake and Exhaust Vents.

Blockages in your outside intake and exhaust can cause airflow problems. Leaves, debris and even the occasional bird can get caught there and impede airflow. Cleaning regularly is a good idea.

There are other possibilities, too: dirty and corrosion of furnace parts or the need to reset the furnace, for example, but this checklist should help you eliminate the most likely possibilities. If you still can’t identify the problem or don’t know how to address it, your HVAC professional will be happy to assist you.

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