Why it happens

Your furnace has two jobs: make heat (the burners) and move it through the house (the blower fan). If you can hear the furnace running but the air coming out of the vents feels cool, one of those two jobs isn't getting done. Here are the usual suspects:

1. The thermostat fan is set to "On" instead of "Auto." The fan runs nonstop, even when the burners are off, so it blows room-temperature air between heating cycles.
2. The filter is clogged. A dirty filter chokes airflow. The furnace can overheat and shut its burners off as a safety measure while the fan keeps running.
3. The flame sensor is dirty. This small metal rod confirms the burners have lit. When it's coated with residue, it can't "see" the flame and shuts the gas off after a few seconds. This is one of the most common furnace calls we get.
4. The ignitor is failing. If the burners can't light, there's no heat.
5. The intake or exhaust pipes are blocked. High-efficiency furnaces use white plastic pipes that run outside. Snow drifts, ice and frost can block them, and the furnace shuts down to protect you.
6. The condensate drain is clogged. High-efficiency furnaces produce water. If the drain line or trap backs up, a safety switch stops the furnace.
7. Airflow problems in the house. Closed or blocked vents, leaky ductwork, or a failing blower motor can all leave some rooms cold.

When to call a professional

Call a licensed technician if:

• You've done the checks above and it's still blowing cool air
• The furnace starts, runs for a few seconds, then shuts off (often a flame sensor or ignition problem)
• You hear banging, squealing or grinding
• You see error lights blinking on the control board
• The furnace keeps shutting down in cold weather

Please don't take apart gas components yourself. Furnace repairs involve gas and electrical parts, and in Alberta that work should be done by a certified gasfitter.

How SS Plumbing & Heating handles it

We start by finding the actual cause, not guessing. We'll check the ignition sequence, flame sensor, ignitor, safety switches, venting, airflow and filter. Then we'll explain what we found and give you a clear price before we fix anything.

Most "running but not heating" problems are repairs, not replacements. A cleaned flame sensor or a new ignitor often gets the heat back on the same visit. If your furnace is unsafe or near the end of its life, we'll tell you honestly. We don't install new furnaces ourselves, so our advice is unbiased, and we'll refer you to trusted installers if you need one. No heat in the middle of the night? We offer 24/7 emergency service, with any after-hours charge quoted upfront.



A Few Questions We Get a Lot

Can a dirty filter really stop my furnace from heating?

Yes. A badly clogged filter can make the furnace overheat, which trips a safety switch that turns the burners off. Replace standard filters every 1–3 months during heating season. Don't want to keep track? We offer furnace filter delivery every 3, 6 or 9 months.

Why does my furnace turn on, then shut off after a few seconds?

This is often a dirty flame sensor or an ignition problem. It's a quick fix for a technician, but it involves gas components, so it's best not to DIY it.

How often should my furnace be serviced?

Once a year, ideally in late summer or fall before Edmonton's heating season starts. Our 20-point tune-up checks everything from the flame sensor and ignitor to gas pressure and venting, and you get a documented inspection report.

Related reading: 5 Common Furnace Problems · The Truth About Furnace Filters · Pre-Winter Home Maintenance Checklist

Still cold?

If you've checked the basics and your house still isn't warming up, we can help. Call or text us, or send a photo of your furnace and any error lights.

Call or Text 780-995-4140 | Book Furnace Repair | Learn more about our furnace repair →