FirstCheck
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🍁 Conçu pour les foyers canadiens — rédigé selon les codes canadiens et les règles provinciales. N’est pas destiné à un usage hors du Canada.
ÉBAUCHE — cette page n’a pas encore été révisée par un professionnel licencié. Aperçu éditorial seulement.

No heat at all (gas furnace)

A furnace that won't make any heat is stressful, especially in January — but the most common causes are free to check and take minutes: the thermostat, a flipped switch, and the filter. Start there before assuming the worst.

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Start at the thermostat. Make sure it's set to HEAT and a few degrees above room temperature, and check the screen: a blank or faded display usually means dead batteries. It feels too simple to be the answer, but it's the most common cause to rule out — and the fix is free.

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visibilityHow to check

  1. Check the screen. Blank, faded, or showing a low-battery icon points to dead batteries — swap them first.
  2. Confirm the mode is HEAT (not OFF or COOL) and the set temperature is at least 3 degrees above the room temperature.
  3. Turn the setpoint up 5 degrees and wait two minutes. A click at the thermostat followed by the furnace starting points away from the thermostat; silence points to it — or to the furnace's power.
buildAucun outil schedule5 min

handymanHow to fix it

Fit fresh batteries, set the mode to HEAT, and raise the setpoint above room temperature. If a smart thermostat lost its schedule or is in an away/eco mode, restore the heat schedule.

  1. Slide the thermostat off its wall plate (most lift straight off) and replace the batteries — usually AA or AAA.
  2. Set the mode to HEAT and the temperature a few degrees above the room.
  3. On a smart thermostat, check it hasn't dropped into an away, eco, or hold mode that's pinning the setpoint low.
schedule10 min savings$0–10

visibilityHow to check

  1. Turn the thermostat up so the furnace tries to start, and watch through the small sight glass in the lower panel. Keep the panels on.
  2. A healthy sequence: the small inducer fan whirs, then an orange glow (the ignitor), then blue flames. No glow and no flame points to the ignitor; flames that light and die within seconds point to the flame sensor.
  3. Let it try — most furnaces attempt ignition three times, then lock out and blink an error code. Note the blink pattern and check the legend printed inside the panel.
buildflashlight schedule15 min

handymanHow to fix it

report Cut the power, and know where the line isKill the power at the furnace service switch before opening the burner compartment — the ignitor runs at line voltage and parts near the burners stay hot long after shutdown. Work on the ignitor and flame sensor only: the moment a job would touch gas piping, the gas valve, or the burners themselves, it's licensed gas-fitter territory in every province. If any of this feels like more than you signed up for, both repairs are quick, inexpensive visits for a pro.

With power off at the furnace switch: replace a failed hot-surface ignitor with the exact matching part, or remove the flame-sensor rod (one screw) and polish it gently with a fine abrasive pad. Never touch the ignitor element with bare fingers, and never disturb the gas piping.

  1. Turn the furnace service switch OFF and close the manual gas shutoff (handle a quarter-turn, crosswise to the pipe), then give the burner area ten minutes to cool.
  2. For the flame sensor: remove its single screw, slide the thin metal rod out, and polish the rod gently with a fine abrasive pad until the metal is bright. Don't bend it. Reinstall snugly.
  3. For the ignitor: unplug its connector, remove the mounting screw, and swap in the exact matching part. The grey element is fragile and skin oils shorten its life — handle it by the base only.
  4. Reseat all panels, turn the switch back on, and watch one full startup through the sight glass. If it locks out again, stop and book a technician — repeated lockouts are the furnace telling you something is still wrong.
schedule40 min savings$15–70
Flame sensor rodMost are near-universal, but match the rod length and mounting bend to the old one Fine abrasive pad (Scotch-Brite type)Fine polishing pad; avoid coarse sandpaper, which pits the rod Hot-surface ignitorMatch your furnace's brand and model number — bring the old ignitor and a photo of the model plate to the parts counter
gavel Vérifiez d’abord votre province AB: permis au propriétaire · BC: permis au propriétaire · ON: permis au propriétaire · PE: permis au propriétaire · QC: réservé aux licenciés
Electrical-side maintenance that does not disturb gas piping, the gas valve, or combustion settings. Anything beyond the ignitor / flame sensor is licensed gas work in every province. REVIEW: confirm this province's position on homeowner work inside the burner compartment.

visibilityHow to check

  1. Find the switch on or beside the furnace — it looks exactly like a light switch, sometimes under a red cover plate, sometimes at the top of the basement stairs. Make sure it's ON.
  2. At the electrical panel, look for a breaker labelled furnace or fan sitting in the middle of its travel — that's tripped.
  3. Check the furnace's front panel door is pushed fully home. A hidden door switch cuts all power when the panel is even slightly ajar.
buildflashlight schedule5 min

handymanHow to fix it

warning If the breaker trips again, stopOne reset is fair game. A breaker that trips a second time is protecting the circuit from a real fault — a failing blower motor, a wiring problem — and resetting it again just reheats the problem. Leave it off and have an HVAC technician or electrician find the fault.

Flip the furnace switch on, reseat the panel door, and reset a tripped breaker by pushing it fully OFF and then back ON. If the breaker trips again, stop — that's a fault, not bad luck.

  1. Turn the furnace service switch ON and press the front panel door firmly into place.
  2. Reset a tripped breaker: push it fully to OFF first (you'll feel it seat), then back to ON.
  3. Give the furnace a few minutes — many run a self-check before starting.
schedule5 min savingssouvent gratuit

visibilityHow to check

  1. Slide the filter out of its slot (between the return duct and the furnace) and hold it up to a light.
  2. If you can't see light through it, it's been choking the furnace. A grey, felted mat of dust is a clear sign.
  3. Look through the sight glass for a blinking status light. A code for "limit trip" or "high temperature" (check the legend inside the panel) supports this cause.
buildflashlight schedule10 min

handymanHow to fix it

Fit a new filter of the same size with the airflow arrow pointing toward the furnace, close everything up, and cycle the furnace switch off and on. Most furnaces recover on their own once they can breathe.

  1. Note the size printed on the old filter's frame (e.g. 16x25x1) and buy the same.
  2. Slide the new filter in with the airflow arrow pointing toward the furnace, and reseat the panel door.
  3. Cycle the furnace service switch off, wait ten seconds, and turn it back on to clear any lockout. If it locks out again with a clean filter, the limit switch may be failing — that one's a pro visit.
schedule10 min savings$10–25
Furnace filter (1-inch or 4-inch media)Match the size printed on your old filter's frame (e.g. 16x25x1); avoid jumping to a much denser filter than the furnace was designed for

visibilityHow to check

  1. Confirm the furnace is a high-efficiency (condensing) model: it will have two white plastic pipes rather than a metal flue. If the flue is metal, rule this cause out.
  2. Look for water pooling at the furnace base, or listen for gurgling when it tries to run — both point to condensate that can't drain.
  3. Follow the small plastic tube from the furnace to the trap (a small plastic box or looped tube) and on to the floor drain. Kinks, algae sludge, or a frozen section along the way are the usual blockages.
buildflashlight schedule15 min

handymanHow to fix it

warning Refill the trap before you restartThe water sitting in the condensate trap isn't just drainage — it's a seal that keeps combustion gases, including carbon monoxide, inside the flue where they belong. Always refill the trap with water before running the furnace, and never disconnect or modify the white vent pipes themselves — vent work is licensed gas-fitter territory.

With the furnace off, remove and rinse the condensate trap, clear the drain line (a wet/dry vacuum works well), refill the trap with water, and reassemble. If a section of the line runs through an unheated space and froze, thaw and re-route or insulate it.

  1. Turn the furnace service switch OFF.
  2. Remove the trap (most twist or pull off), rinse the sludge out in a sink, and flush the drain line — a wet/dry vacuum on the line's outlet end pulls clogs through cleanly.
  3. Refill the trap with clean water before reinstalling it.
  4. Reassemble, turn the power back on, and watch one heating cycle: water should trickle steadily to the drain with no pooling.
schedule30 min savings$0–20

verifiedPourquoi confier ceci à un pro

Confirming a failed gas valve or control board means testing live gas controls and line voltage, and replacing a gas valve means opening and re-sealing gas connections. In every Canadian province this is work reserved for a licensed gas-fitter. You've done your part by ruling out the simple causes — that homework makes the technician's visit faster and cheaper.

gavel Vérifiez d’abord votre province AB: réservé aux licenciés · BC: réservé aux licenciés · ON: réservé aux licenciés · PE: réservé aux licenciés · QC: réservé aux licenciés
Gas valve and combustion-control replacement is licensed gas-fitter work in every Canadian province.

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Pourquoi la liste est dans cet ordre

Nous ne classons pas seulement selon la probabilité. Nous classons comme le ferait un bon artisan honnête : éliminer d’abord les causes gratuites, sûres et courantes. C’est pourquoi les vérifications peu coûteuses passent avant les réparations chères — et pourquoi tout ce qui est dangereux reçoit un arrêt net plutôt qu’un encouragement. Cet ordre existe pour vous faire économiser, pas pour vous vendre quelque chose.