By Mario Vaghei, General Manager, Aire One Peel Heating & Cooling · Published November 9, 2026 · Facts verified November 5, 2026
Short answer
Some problems cannot wait. If you smell gas, leave the house and call Enbridge Gas at 1-866-763-5427 or 911 from outside. If a carbon monoxide alarm sounds, get everyone out and call 911. Smoke, or a burning electrical smell, is also a tonight problem. Most other things can be made safe and booked for the next day: a noise, a furnace that short cycles, a small drip, an air conditioner that stops on a mild night. No heat in freezing weather sits in between, and the checks below help you decide.
On this page
Act now: leave first, call second · Call now or wait: a quick table · No heat at night: four checks before you call · If you rent · Air conditioning at night · When to call us · Frequently asked questions
Act now: leave first, call second
- You smell gas. Leave the house. Do not use light switches or phones inside. From outside, call Enbridge Gas at 1-866-763-5427 or 911.
- A carbon monoxide alarm is sounding. Get everyone out and call 911 from outside. Do the same if people have headaches, nausea or dizziness that ease in fresh air. Our guide to furnace carbon monoxide in Ontario explains the signs.
- You see smoke or flames, or smell burning plastic or wiring. Leave and call 911.
Ontario's carbon monoxide rules, in effect January 1, 2026, call for an alarm on every storey of the home, including storeys that have no sleeping areas. Ontario.ca explains which homes this covers.
Call now or wait: a quick table
| What is happening | Tonight | Can it wait? |
|---|---|---|
| Smell of gas | Leave; call Enbridge Gas or 911 from outside | No |
| Carbon monoxide alarm sounding | Everyone out; call 911 | No |
| Smoke, or a burning plastic or wiring smell | Leave; call 911 | No |
| Dusty burning smell the first time the furnace runs in fall | Open a window; it should fade | Yes, if it fades. If it does not, switch the furnace off and book a visit |
| Water near the furnace's wiring | Switch the furnace off at the thermostat and the service switch; wipe up the water | Book for the next day |
| No heat, and it is well below freezing | Run the checks below; keep the house closed up | If the checks do not bring heat back, call for service rather than waiting |
| Furnace turns on and off every few minutes | Check the filter; leave it running if the house is holding temperature | Usually yes; book a visit |
| New rattle, bang or squeal | Note when it happens | Usually yes; switch off if it is loud or getting worse |
| Air conditioner stops on a mild night | Switch it off; open windows | Yes |
Table: gas and carbon monoxide steps from Enbridge Gas and ontario.ca (read October 26 and September 24, 2026, re-checked November 5, 2026); the rest is general guidance, and our linked guides give the detail.
More detail on three of these: a burning smell from a furnace, a furnace leaking water and furnace short cycling.
No heat at night: four checks before you call
- Thermostat. Is it set to heat, with the temperature above the room temperature? Are the batteries good?
- Furnace switch and breaker. The service switch near the furnace looks like a light switch and is easy to turn off by mistake. Check the breaker too.
- Filter. A badly clogged filter can make a furnace shut itself down.
- Outside vents. On a high-efficiency furnace, clear snow or ice from the plastic intake and exhaust pipes on the outside wall.
If none of these brings the heat back and it is freezing outside, do not wait: pipes can freeze in an unheated house. Do not use an oven, a barbecue or a camp stove for heat. Our page on who to call for emergency furnace repair in Mississauga covers the next step.
If you rent
Heat is your landlord's responsibility. Under Ontario Regulation 516/06 of the Residential Tenancies Act, heat is a vital service from September 1 to June 15, and the landlord must keep the unit at 20°C or more, measured 1.5 metres above the floor and at least 1 metre from the exterior walls. The rule does not apply where the tenant controls the temperature and the heating system is able to hold 20°C. Your city may also have its own temperature by-law, so check your city's website. Tell your landlord right away and keep a note of the time.
Air conditioning at night
A cooling problem is rarely urgent on a mild night. Switch the system off, open windows, and book a visit. It becomes urgent when it is very hot and someone in the home is vulnerable to heat. Our guide to when AC repair is an emergency goes through it.
When to call us
For anything on the "act now" list, call 911 or Enbridge Gas first. For everything else, call 905-564-8545 to book furnace repair in Mississauga. Tell us what you saw, heard and smelled, and what you have already checked.
Frequently asked questions
Should I call for furnace repair at night or wait until morning?
Do not wait if you smell gas, a carbon monoxide alarm is sounding, or you see smoke or smell burning wiring: leave and call from outside. If there is no heat in freezing weather and the basic checks do not help, call for service. Noises, short cycling and small drips can usually be booked for the next day.
What should I do if I smell gas at night?
Leave the house right away without using light switches or phones inside. From outside, call Enbridge Gas at 1-866-763-5427 or 911.
What should I do if my carbon monoxide alarm goes off at night?
Get everyone out of the house and call 911 from outside. Do not go back in until emergency services say it is safe.
My furnace stopped working at night. What can I check myself?
Check that the thermostat is set to heat, that the furnace's service switch and breaker are on, that the filter is not clogged, and that the outside intake and exhaust pipes are clear of snow and ice.
How warm does my landlord have to keep my apartment in Ontario?
Under Ontario Regulation 516/06, from September 1 to June 15 a landlord must keep a rental unit at 20°C or more, unless the tenant controls the temperature and the heating system is able to hold 20°C. Your city may also have its own by-law.
Sources and references
- Enbridge Gas, "Smell gas?", read November 5, 2026.
- Government of Ontario, "Carbon monoxide safety", read November 5, 2026.
- Ontario Regulation 516/06 (General), Residential Tenancies Act, 2006, section 4, read November 5, 2026.