First, the two-minute version
Before calling anyone, check six things: the thermostat is on Heat and set above room temperature, the furnace switch and breaker are on, the filter isn’t plugged, the exterior intake and exhaust pipes aren’t blocked by frost or snow, the furnace door is fully seated, and the condensate line isn’t frozen. These six checks resolve a surprising share of “no ignition” calls — safely, and for free.
It’s -30, the furnace is clicking but not lighting, and the house is already cooling. Deep breath. Some of the most common causes of a no-ignition furnace in a Calgary cold snap are things you can check yourself in ten minutes without tools and without touching anything that burns gas. Here’s the sequence we walk callers through on the phone, in the order that finds the problem fastest.
Is it actually getting the call for heat?
Start at the thermostat, not the furnace. Confirm it’s set to Heat — not Off, not Cool — and push the setpoint 3–4 degrees above the current room temperature so it’s unambiguously calling. If the screen is blank, replace the batteries; a dead thermostat is one of the cheapest “no heat” causes there is. Smart thermostats can also lose their Wi-Fi mind occasionally — pull it off the wall plate and reseat it.
Next, power. Furnaces have a switch on or near the unit that looks exactly like a light switch, and it gets bumped off more often than you’d think — especially in storage-crowded basement rooms. Check it, then check the breaker panel for a tripped breaker. If a breaker trips again immediately after reset, stop and call; that’s an electrical fault, not a nuisance trip.
Are your intake and exhaust pipes frozen over?
This is the big one at -30, and it’s a Calgary specialty. High-efficiency furnaces breathe through two plastic pipes that exit the side of your house. In extreme cold, the moisture in the exhaust can build frost or ice right over the pipe openings — and drifting snow can bury them. When the pipes block, a safety switch (the pressure switch) correctly refuses to let the furnace light, and you get click-click-nothing followed by a lockout.
Go outside and find the two pipes — usually white PVC on the side or back of the house, often near the gas meter. Clear any snow, knock off frost and ice around the openings, and make sure nothing else is obstructing them. We take these calls all winter in Somerset, Millrise, and Bridlewood, where prevailing winds love to drift snow against certain exposures. If clearing the pipes fixes it, the furnace usually relights within a few minutes once you cycle the power.
When did you last change the filter?
A fully loaded filter chokes airflow, overheats the furnace, and trips the high-limit switch — which shuts the burners down mid-cycle or prevents clean ignition in the first place. If the filter looks like grey felt, swap it. In a Calgary winter with the furnace running near-constantly, 1-inch filters can plug in a month. After changing it, turn the furnace switch off for 30 seconds and back on to clear the lockout, then let it attempt ignition.
Is the blower door fully closed?
The lower access panel on your furnace presses a small safety switch when seated. If the door is even slightly ajar — say, after someone changed a filter in a hurry — the furnace won’t run at all. Push the panel firmly until it seats. This one is free, takes ten seconds, and is more common than anyone likes to admit.
What do the clicks and flashes mean?
Modern furnaces tell you what’s wrong if you know how to listen.
| What you notice | Most likely story | Your move |
|---|---|---|
| Clicking, no flame, then shutdown | Igniter or flame sensor trouble | Check filter and vents, then call |
| Fires up, dies after a few seconds | Dirty flame sensor | A tech call — quick, inexpensive fix |
| Humming, never attempts ignition | Inducer motor or pressure switch | Check exterior pipes, then call |
| Nothing at all, no sounds, no lights | Power, switch, breaker, or board | Check switch and breaker, then call |
| Status LED blinking a pattern | Error code | Count the flashes; the legend is on the door panel — tell us the code when you call |
What should you never try yourself?
Everything above is safe. The following are not, and at -30 the stakes are too high for improvisation:
- Don’t open the burner compartment or attempt to clean the flame sensor, igniter, or burners yourself unless you genuinely know the procedure. Igniters are fragile and gas components are unforgiving.
- Don’t bypass or jumper any safety switch. Those switches are the only thing standing between a fault and a carbon monoxide problem.
- Don’t repeatedly force reset cycles. Two or three attempts, fine. Twenty attempts floods the story and tells us nothing except that the furnace is now in hard lockout.
- If you smell gas, stop. Leave the house, then call your gas utility’s emergency line and then us, from outside.
Meanwhile, protect the house: keep taps at a trickle if the indoor temperature is falling fast, open cabinet doors on exterior-wall plumbing, and close off unused rooms. Frozen pipes are the expensive sequel to a no-heat night.
Still no heat? That’s what our 24/7 line is for
If you’ve run the checklist and the furnace still won’t light, it’s a genuine repair — most often an igniter, flame sensor, or pressure switch at this time of year. Comfort Environment answers (403) 888-1578 around the clock, every day of the winter, across Calgary’s southwest. Tell us what you checked and what the furnace is doing; it shortens the visit and gets your heat back sooner.
Frequently asked questions
Why does my furnace stop working only when it gets really cold?
Extreme cold exposes weaknesses: exterior intake and exhaust pipes frost over, marginal igniters fail under continuous duty, and furnaces running near-constantly overheat if the filter is loaded. The -30 stretch is when every borderline component finally gives out.
How do I reset my furnace after a lockout?
Turn the furnace power switch (the light-switch-style toggle on or near the unit) off, wait 30 seconds, and turn it back on. The furnace will retry ignition. If it locks out again after two or three attempts, stop resetting and call a technician — repeated forced retries can worsen the problem.
Can a frozen exhaust pipe really shut down a furnace?
Yes. High-efficiency furnaces vent through exterior PVC pipes, and frost, ice, or drifted snow over the openings blocks airflow. The pressure switch then prevents ignition as a safety measure. Clearing the pipe openings and power-cycling the furnace often restores heat immediately.
How long before pipes freeze in a house with no heat?
At -30 with wind, an average home can drop toward freezing indoors within roughly 24 hours, and pipes in exterior walls or unheated areas are at risk sooner. Trickle taps, open cabinet doors on plumbing walls, and treat no-heat as urgent rather than a wait-until-morning problem.