Furnace Not Working? 8 Things to Check Before You Call

A furnace that stops working on a cold Ottawa night is stressful. Before you call, there are a few safe things you can check yourself. Some of them fix the problem outright, and the rest help the technician get to the cause faster.

First: safety

• If you smell gas (a rotten-egg smell), don't touch light switches or the thermostat. Leave the house, then call Enbridge Gas's emergency line at 1-866-763-5427 or 911 from outside.
• If your carbon monoxide alarm goes off, get everyone out and call 911. Don't go back in until you're told it's safe.

Everything below assumes there's no gas smell and no CO alarm.

1. Check the thermostat

Make sure it's set to Heat, set a few degrees above the room temperature, and that the screen is on. Many thermostats run on AA batteries, and a dead battery is one of the most common "no heat" calls.

2. Check the furnace switch and breaker

Most furnaces have a switch that looks like a light switch on or near the unit, and it's easy to flip off by accident. Check that it's on, and that the furnace breaker in your electrical panel hasn't tripped.

3. Make sure the front panel is closed

Furnaces have a safety switch that stops them running if the access door isn't seated properly. If someone changed the filter recently, push the panel firmly into place.

4. Check the filter

A badly clogged filter can make a furnace overheat and shut itself off. If it's grey and caked with dust, replace it and give the furnace a few minutes to restart.

5. Check the outdoor vent pipes

This one is very Ottawa. High-efficiency furnaces vent through two white plastic pipes on the side of the house. If snow or ice has drifted over them, the furnace will shut down for safety. Gently clear the snow from around both pipes.

6. Look for water around the furnace

High-efficiency furnaces produce water that drains away through a small hose. If the drain is blocked or frozen, the furnace may stop. Water pooling under the unit is a sign to call.

7. Note the error code

Most modern furnaces have a small light that blinks a code when something's wrong, with a chart on the inside of the panel. Write down the pattern before you call. It saves time.

8. Don't keep resetting it

If the furnace starts and then shuts off again, resist the urge to keep cycling the power. Repeated resets can hide the real problem, and some faults are safety lockouts for good reason.

When to call

If none of the above gets the heat back on, or the furnace is making new noises, cycling on and off, or blowing cold air, it's time for a furnace repair visit. If your furnace is getting on in years and the repairs keep coming, read our guide on repairing versus replacing a furnace. And a yearly furnace tune-up catches most of these problems before the first cold snap.