Furnace Not Heating? 6 Things to Check Before You Call

Short answer: Set the thermostat to HEAT and a few degrees above room temperature, confirm the furnace power switch and breaker are on, replace a clogged filter, and make sure return and supply vents are open. If the furnace still won't fire — or you ever smell gas — turn it off and call a licensed technician right away.

1. Check the thermostat

Make sure it's on HEAT, set above the current room temperature, and that the batteries (if any) are fresh. A blank or unresponsive thermostat is a common false alarm.

2. Confirm power to the furnace

Most furnaces have a standard light-switch-style power switch nearby — it can get flipped off by accident. Also check the breaker panel for a tripped breaker.

3. Replace a dirty filter

A clogged filter starves the furnace of airflow and can trip its safety limit, shutting it down. Check the filter monthly during heating season.

4. Make sure vents are open and clear

Blocked returns or closed supply registers reduce airflow and can cause short-cycling. Keep furniture and rugs off your vents.

5. Look at the furnace status light

Many furnaces flash a diagnostic code through a small window. Note the pattern — it helps your technician arrive ready with the right part.

6. If you smell gas — stop

If you smell gas (rotten-egg odour), do not touch switches. Leave the home and call your gas utility's emergency line, then call us. Energy Clean offers 24-hour heating service across the GTA.