A furnace that stops working on a cold Hamilton night is stressful. Before you book a service call, a few simple checks can sometimes get the heat back on, and they’ll help our technician diagnose the problem faster if you do need us.
Safety first: if you smell gas (a rotten-egg smell), hear your carbon monoxide alarm, or see scorch marks or smoke, don’t troubleshoot. Leave the house and call 911 from outside.
1. Check the thermostat
- Make sure it’s set to Heat, not Cool or Off.
- Set the temperature a few degrees above the current room temperature.
- Check that the fan is set to Auto. “On” runs the fan constantly, even when the burners are off, so you’ll feel cool air between cycles.
- Replace the batteries if the screen is blank or dim.
- For smart thermostats, check for a schedule, an “eco” or “away” mode, or a lost Wi-Fi connection.
2. Check the furnace filter
A clogged filter starves the furnace of air. It can overheat and shut the burners off as a safety measure, so you get cold air or short cycling. Hold the filter up to a light: if you can’t see through it, replace it.
3. Check the power switch and breaker
Most furnaces have a service switch that looks like a light switch, on or near the furnace. Make sure it’s on. Then check your electrical panel for a tripped furnace breaker. If the breaker trips again, leave it off and call us.
4. Make sure the blower door is closed
Furnaces have a safety switch that stops the furnace from running when the front panel isn’t seated properly. After changing a filter, make sure the panel is fully closed.
5. Clear the outdoor vent pipes
High-efficiency furnaces vent through white plastic (PVC) pipes on an outside wall. Snow drifts, ice or a bird’s nest can block them, and the furnace will shut down. Carefully clear snow and ice away from both pipes.
6. Check the condensate drain
High-efficiency furnaces produce water that drains through a small hose or into a condensate pump. A clogged drain, a frozen line or a full pump can shut the furnace off. Look for water around the furnace or a pump that’s full.
7. Make sure the gas is on
Check that the gas valve to the furnace is open (the handle runs parallel to the pipe). If other gas appliances such as the stove or water heater also aren’t working, contact your gas utility.
8. Open the supply vents and return grilles
Closed or blocked vents make some rooms cold and can make the furnace overheat. Keep at least most vents open and don’t block return grilles with furniture.
9. Note any error codes or noises
Many furnaces have a small light that blinks a code through a window in the panel. Write it down, along with any noises (banging, squealing, rumbling) and when they happen. It helps our technician arrive with the right parts.
When to call a professional
Call a licensed technician if:
- The checks above don’t fix it, or the problem keeps coming back.
- The furnace turns on and off rapidly (short cycling).
- You hear banging, grinding or squealing.
- The burner flame is yellow or flickering instead of steady blue.
- Your furnace is over 15 years old and needing more frequent repairs. It may be time to look at furnace replacement.
Lancaster Heating and Cooling offers 24/7 emergency furnace repair across Hamilton, Halton and Niagara. Call 905-388-3333.
Regular furnace maintenance prevents many of these problems before they start.
