Most furnaces need a few minutes to restart after the power comes back, and many won't run until the thermostat calls for heat again. If the power has been steady for a while and the furnace still won't start, check the thermostat, the furnace switch and the breaker, try one reset, then call. Don't keep cycling the power.
Safety first: If a CO alarm goes off, leave the home now and call 911 from outside. If you smell gas, leave and, from outside, call 911 and Enbridge Gas's emergency line at 1-866-763-5427. On propane, call 911 and your propane supplier.
Why did my gas furnace stop when the power went out?
A gas furnace burns gas for heat, but it also uses electricity. Natural Resources Canada's guide to heating with gas describes furnaces with electric ignition and electric blower motors, which move warm air through the ducts. A furnace like that can't run without power. Ontario and federal outage guidance both warn that you may lose heat during an outage, so a furnace that stops when the lights go out is expected.
The power is back. Why is the furnace still off?
Often it just needs time. When power returns, the thermostat and the furnace both restart, and many furnaces run through a short safety sequence before they light. If you turned the thermostat down during the outage, as official guidance suggests, it won't call for heat until you turn it back up. A tripped breaker, a switch left off, or a lockout from a failed start can also keep it quiet.
Give the power time to settle
The Government of Ontario's power outage guidance says to wait 10 to 15 minutes before slowly turning appliances back on, and to turn the essentials on first, such as the heat in winter. The federal power outage page also says to turn the heating thermostats up first. After a storm, power can flicker on and off before it holds, so wait until it stays on.
What should I check first once the power is steady?
Start at the thermostat. Make sure it's set to heat and a few degrees above the room temperature. Some thermostats take a minute to start up after an outage, and some wait a few minutes before they call the furnace. If the screen is blank or the settings were lost, our guide for when the thermostat says heat but the furnace won't start walks through it.
Then check the furnace's power
- Find the furnace switch. It often looks like a light switch on a wall or post near the furnace. Make sure it's on.
- Check for a tripped breaker labelled furnace. Only do this with dry hands, standing on a dry floor. Reset a tripped breaker once. If it trips again, leave it off and call.
- Make sure the furnace door is closed tight. Many furnaces won't start with the door open.
Our furnace not working checklist covers the filter and status lights if those three look fine.
Is it safe to reset the furnace after an outage?
One reset is reasonable once the power has been steady for a while. Turn the furnace switch off, wait a minute, then turn it back on, and give the furnace several minutes to try. If it still doesn't heat, or it starts and then shuts down again, stop and call. Repeated resets send the furnace through more failed starts and can hide the real problem.
Stop and call if
- The breaker trips again
- The furnace tries to light and then shuts down
- You hear new grinding, banging or buzzing
- You smell burning or hot wiring
- A status light keeps flashing after one reset
If you hear clicking or a fan but there's no flame, see our guide for a furnace that won't ignite. Write down what the status light does before you reset, since losing power can clear the stored code.
What if only my home lost power?
Check with your neighbours. If their lights are on and yours aren't, the problem may be at your home rather than on the grid. The federal outage page says to check whether the outage is only in your home, to check your breaker panel or fuse box, and to report outages to your power company. Don't open any electrical equipment. If something looks damaged, Ontario's guidance says to contact an electrician.
How do I stay warm safely until the heat comes back?
Never heat your home with a generator, BBQ, camping stove, gas stove or oven. Ontario's power outage guidance warns that using a gas stove or oven for heat could lead to carbon monoxide poisoning, and that the exhaust from BBQs, camping stoves and home generators used indoors can be fatal. The federal extreme cold guidance says never to run a generator inside a home, garage, basement, crawlspace or shed.
Use only space heaters made for indoor use, and keep battery-powered CO alarms working, since plug-in alarms without a battery backup stop during an outage. If the home is too cold and it's safe to leave, go somewhere warmer. For space heater spacing, keeping pipes from freezing and when to leave, see our guide to waiting for furnace repair.
When should I call for emergency furnace repair?
Call when the power has been steady, you've done the basic checks and one reset, and there's still no heat. Call sooner if the house is getting cold, someone at home is very young, older or unwell, or the temperature outside is dropping fast. Furnace Repair Barrie answers 24/7 at (249) 209-2216. See our 24/7 emergency furnace repair page for what to have ready.
Tell us
- When the power went out and when it came back
- Whether the power flickered on and off
- What the thermostat shows
- Any resets you tried and what happened
- The status light pattern, if there is one
- Your fuel (natural gas, propane or oil) and your town