Furnace Not Turning On? 7 Things to Check Before You Call

A furnace that will not come on in a Calgary winter feels like an emergency, and sometimes it is. But a good share of no-heat calls come down to something you can check in fifteen minutes without tools. Work through these in order. If you smell gas at any point, stop and skip to the end.

1. The thermostat

Make sure it is set to Heat, not Off or Cool, and set a few degrees above the room temperature. If the screen is blank or dim, replace the batteries. Smart thermostats can drop into an away or eco mode after a power blip, so check that too.

2. The furnace switch

Most furnaces have a power switch that looks exactly like a light switch, on the furnace itself or on a wall or stairwell nearby. It gets bumped off more often than people expect.

3. The breaker

Check the electrical panel for a tripped breaker labelled furnace. Reset it once. If it trips again, leave it off and call.

4. The front panel

A safety switch keeps the furnace from running if the blower door is not seated properly. If someone changed the filter recently, push the panel firmly back into place.

5. The filter

A badly clogged filter starves the furnace of air. It can overheat and shut itself down to stay safe. If the filter is grey and caked, replace it. Through a Calgary winter, check it monthly.

6. The vent pipes outside

High-efficiency furnaces breathe through two white plastic pipes on an outside wall. Drifting snow, frost or ice can block them, and the furnace shuts down for safety. Clear them by hand. After a big snowfall or a deep cold snap, this is a classic Calgary no-heat call.

7. The condensate drain

High-efficiency furnaces make water and drain it away through a small tube, often to a floor drain or a small pump. If that line is blocked or frozen, or the pump is full, a float switch shuts the furnace off. Water pooling around the base of the furnace is the clue.

Check the status light before you call

Most modern furnaces have a small window with a blinking light. The pattern is an error code, and the chart that explains it is usually printed on the inside of the panel. Write the pattern down before you call. It speeds up the diagnosis.

Resetting the furnace

Turning the furnace switch off for 30 seconds and back on lets it try again. Once is fine. If it locks out again, do not keep cycling it. A safety control is telling it to stop, and that needs a gasfitter.

If you smell gas

Do not touch light switches or the thermostat. Get everyone out of the house, then call 911 and ATCO's 24-hour gas emergency line at 1-800-511-3447 from outside.

While you wait for the repair

Keep the house above about 15°C with space heaters plugged straight into the wall, not into extension cords. Open the cabinet doors under sinks on outside walls. Our frozen pipes guide has the rest.

Common questions

Why does my furnace start, then shut off?

That is short cycling. The usual causes are a dirty filter, a blocked vent pipe, a dirty flame sensor or the furnace overheating. If a new filter and clear vents do not fix it, it needs a service call.

Is it safe to reset my furnace?

Once, yes. Repeated lockouts mean a safety control keeps tripping, and the cause needs to be found, not reset around.

Can a plumber fix my furnace?

A plumber who is also a certified gasfitter can. Here is how that credential works in Alberta.