furnace runs constantly – Aire One East Heating & Cooling https://www.aireonedurham.ca Wed, 21 Oct 2026 10:01:43 +0000 en-CA hourly 1 https://wordpress.org/?v=7.1.3 https://www.aireonedurham.ca/wp-content/uploads/2020/06/fav-img.png furnace runs constantly – Aire One East Heating & Cooling https://www.aireonedurham.ca 32 32 Furnace Won’t Turn Off? Why It Runs Constantly and How to Fix It https://www.aireonedurham.ca/furnace-wont-turn-off/?utm_source=rss&utm_medium=rss&utm_campaign=furnace-wont-turn-off Wed, 21 Oct 2026 10:00:31 +0000 https://www.aireonedurham.ca/?p=14065 Aire One East Heating & Cooling Furnace Won’t Turn Off?Why It Runs Constantly First find out if it is the fan or the heat that keeps running, then try these safe checks before you call 7 Common CausesSafe DIY ChecksDurham Region 2026 GUIDEAIRE ONE EASTDURHAM REGION ★ 4.8 Google (364)Carrier Factory Authorized24/7 Emergency ServiceFamily Owned Since 1991TSSA Licence #1219734Serving Durham Region Updated October 21, 2026 · Reviewed by Ben Amina, TSSA-certified gas technician, Licence #1219734 · Aire One East Heating & Cooling By Ben Amina, Owner and Manager · TSSA Licence #1219734Aire One East Heating & Cooling, 1910 Dundas St E #117, Whitby When your furnace won’t turn off, the first question is what exactly keeps running: the fan, or the heat. If only the fan runs and the air from the vents feels cool or room temperature, the cause is usually a thermostat fan set to ON, a stuck blower relay, or a fan limit switch. If warm air keeps blowing and the house is getting hotter than the setting, the burners are not shutting off, which can point to a thermostat fault or, rarely, a stuck gas valve. This guide walks through the seven most common causes, the safe checks you can do in a few minutes, and when to call a licensed technician. For problems with the thermostat itself, see our thermostat not working guide. Key takeaways When a furnace won’t turn off, start by checking whether it is the fan or the heat that keeps running, because the causes are different. A thermostat fan set to ON instead of AUTO is the most common reason a furnace seems to run nonstop. A stuck blower relay, a faulty control board, or a fan limit switch can keep the fan running after the heat shuts off. Long run times during a Durham cold snap can be normal, but a furnace that never reaches the setting may be undersized or losing heat through leaky ducts. If the burners will not shut off and the house keeps getting hotter, turn the furnace off at its power switch and call a technician. Short answer: a furnace won’t turn off most often because the thermostat fan is set to ON, the thermostat setting or wiring is calling for heat nonstop, or a stuck blower relay or fan limit switch keeps the fan running. Dirty filters, leaky ducts, and an undersized furnace can also make it run far longer than normal. Set the fan to AUTO and lower the temperature first. If it still runs, switch the furnace off at its power switch and call a licensed technician. Aire One East offers 24/7 heating service across Durham Region. Call 905-576-7600. On this page Why won’t my furnace turn off? Fan or heat: what keeps running when a furnace won’t turn off? 7 reasons a furnace won’t turn off How long should a furnace run? Causes at a glance Quick checks you can do safely When a furnace won’t turn off, call a pro Key terms in this article Frequently asked questions Why won’t my furnace turn off? A furnace runs in cycles. The thermostat calls for heat, the burners light, the blower pushes warm air through the house, and when the room reaches the setting, the thermostat stops calling for heat. The burners shut off, the blower runs a little longer to pull the last heat out of the heat exchanger, and then everything goes quiet. When your furnace won’t turn off, something in that chain is stuck on: the thermostat keeps calling for heat, a switch or relay keeps the blower running, or the house is losing heat so fast that the furnace can never catch up. Knowing which part is stuck tells you whether it is a quick fix or a service call. Fan or heat: what keeps running when a furnace won’t turn off? When a furnace won’t turn off, hold your hand over a supply vent. If the air is cool or room temperature and the furnace is quiet apart from the blower, only the fan is running. That points to the fan setting, a blower relay, or a fan limit switch. If the air is warm and the house is getting hotter than the thermostat setting, the burners are still firing. That points to the thermostat, its wiring, or the control board, and in rare cases a gas valve that is not closing. A furnace that runs warm air for hours but never warms the house to the setting is a third case, usually caused by airflow, heat loss, or sizing. A fan set to ON instead of AUTO is the most common reason a furnace seems to run nonstop. Check it first. 7 reasons a furnace won’t turn off 1. The thermostat fan is set to ON With the fan set to ON, the blower runs all the time, even when the burners are off, so it sounds like the furnace never stops. Switch the fan setting to AUTO, and the blower will run only during heating cycles. That one change fixes most calls where a furnace won’t turn off. This is also why the air can feel cool between cycles, which we cover in our furnace blowing cold air guide. 2. A thermostat setting, location, or wiring problem If the thermostat is set much higher than the house can reach, the furnace won’t turn off because it keeps trying to get there. A thermostat in a drafty hallway or near an outside door may read colder than the rest of the house, and a weak battery, a failing thermostat, or a shorted thermostat wire can keep calling for heat. Try lowering the setting by a few degrees. If the furnace still keeps running with the thermostat switched to OFF, the problem is likely the wiring or the control board. Our guide to winter thermostat settings explains sensible temperatures. 3. A stuck blower relay or faulty control board The control board uses a relay to switch […]

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