Furnace Not Turning On: What to Check

Furnace not turning on, or running but blowing cold air? Most no-heat calls come down to the thermostat, power, a door switch, a clogged filter or a blocked vent. Here are the safe checks a homeowner can do first, and when to call a licensed technician.

Homeowner with a furnace problem? Call (647) 657-2977 or book a service call — licensed technicians across Vaughan and the GTA.

Common reasons: furnace not turning on

• Thermostat set wrong or dead thermostat batteries
• Furnace switch or breaker off
• Front door panel not closed (safety switch open)
• Clogged air filter tripping the high-limit switch
• Snow, ice or debris blocking the outside intake or exhaust pipes
• Ignition, flame sensor, pressure switch or control board fault (shown as a flashing code)

Safe checks you can do yourself

1. Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
2. Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
3. Make sure the furnace front door or panel is closed properly; many furnaces will not run with the door switch open.
4. Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
5. Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
6. Check that the gas valve next to the furnace is open (handle in line with the pipe). Do not force it.
7. Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

When to call a licensed technician

• The furnace light is flashing a code
• You hear clicking but the burners never light, or they light and go out
• The furnace shuts off again after a reset
• You smell gas or something burning (leave the house and call from outside if you smell gas)

Showing an error code? Look it up by brand

AirQuest FurnaceCarrier FurnaceDaikin FurnaceGoodman FurnaceICP FurnaceKeepRite FurnaceLennox FurnaceMidea FurnaceRheem FurnaceRinnai Wall FurnaceTrane FurnaceYork Furnace

Detailed troubleshooting guides

• Blowing cold air All brands · Furnace
• No heat All brands · Furnace
• Short cycling All brands · Furnace
• Burners will not light or stay lit - Carrier 58SB0A/58SB1A Carrier · Furnace
• Furnace not responding to thermostat - Carrier 58SB0A/58SB1A Carrier · Furnace
• Control display blank, furnace dead - Daikin DR96TN/DD96TN Daikin · Furnace
• Furnace not paired with R-32 cooling - disable A2L function - Daikin DR96TN/DD96TN Daikin · Furnace
• No heat - Daikin DR96TN/DD96TN Daikin · Furnace
• Control display blank, furnace dead - Goodman/Amana 9-speed ECM furnaces Goodman · Furnace
• No heat - Goodman/Amana 9-speed ECM furnaces Goodman · Furnace

Furnace not turning on: questions homeowners ask