Furnace Not Turning On? What to Check Before You Call

It's cold, the thermostat is calling for heat, and nothing is happening. Before you book a service call, there are a few safe things worth checking yourself. A lot of no-heat calls come down to one of them. Here's the list, and the point where you should stop and call a technician.

First: when not to troubleshoot

• You smell gas. Leave the house right away and call your gas utility's emergency line from outside. Don't flip switches or try to relight anything.
• Your carbon monoxide alarm is going off. Get everyone outside and call 911.

If neither of those applies, work through the checks below. None of them need tools.

1. Check the thermostat

Make sure it's set to Heat, and that the set temperature is a few degrees above the room temperature. If the screen is blank, replace the batteries. Check that a schedule or vacation hold hasn't turned the temperature down, and that the fan is set to Auto instead of On, or it will blow unheated air between cycles.

2. Check the furnace switch

Most furnaces have a power switch on or near them that looks just like a light switch. It gets bumped or switched off by accident more often than you'd think. Make sure it's on.

3. Check the breaker

Find the furnace breaker in your electrical panel. If it has tripped, switch it fully off, then back on. If it trips again, leave it off and call. A breaker that won't stay on is telling you something.

4. Check the furnace filter

A clogged filter chokes the airflow. The furnace overheats, its safety control shuts it down, and it can keep doing that until the filter is changed. Slide the filter out and hold it up to the light. If you can't see through it, replace it.

5. Check the furnace door

The front panel has a safety switch behind it, so the furnace won't run if the panel is loose or off. If the filter was changed recently, make sure the door is seated properly.

6. Check the vents outside

A high-efficiency furnace breathes through plastic pipes that come out the side of the house. If snow, ice, frost, leaves, or a nest blocks them, the furnace shuts itself off. Clear anything away from the pipe ends, and keep the snow shovelled back from them in winter.

7. Check the gas supply

Look at the gas shutoff on the pipe beside the furnace. The handle should run in line with the pipe. If your other gas appliances, like the stove or hot water tank, aren't working either, the problem is the gas supply to the house and not the furnace.

8. Look for a flashing light

Most modern furnaces have a small light, visible through a window in the door, that flashes a code when something is wrong. Count the flashes and write the pattern down. There's usually a chart inside the door that explains it, and it's the first thing a technician will ask you.

You can try one reset: switch the furnace off at its switch, wait a minute, and switch it back on. If it doesn't start and stay running, don't keep resetting it.

When to stop and call

• The breaker trips again after you reset it
• The furnace starts, then shuts off again within a few minutes
• There's water pooling around the furnace
• You notice a burning smell that doesn't clear
• The same error code keeps coming back
• You've been through the list and there's still no heat

That's the point where it needs a certified technician. Our team handles furnace repair across Lethbridge and the surrounding towns. Send a service request, or call or text 403-915-4328, and tell us what you found. It helps us show up with the right parts.

If the heat will be off for a while

• Keep outside doors and the garage door closed, and close the blinds at night
• Open the cabinet doors under sinks on outside walls, and let a tap run at a trickle, to help keep pipes from freezing
• If you use an electric space heater, keep it clear of anything that can burn and don't leave it running unattended
• Never heat the house with a gas stove, oven, or BBQ

If a pipe does freeze or burst, shut off the main water valve and see our plumbing services.

How to avoid the no-heat call

Check your filter once a month through heating season and change it when it's dirty. Keep the outdoor vents clear. And have the furnace serviced once a year, ideally in the fall. A furnace service catches worn parts before they quit on the coldest night of the year.

If your furnace is 15 or more years old and the repairs are adding up, it may be time to look at furnace replacement. Every Trane furnace we install comes with a free ecobee smart thermostat, so see the Trane offer. Own a mobile or manufactured home? Those need approved models, so read what to know about mobile home furnace replacement.