What it usually means, the likely causes in order, what to safely try first, what a pro charges in Canada, and when to stop and call one.
This guide covers the common cases. Describe your exact problem and get a personalized diagnosis — free to start, with a DIY vs. call-a-pro verdict and a real cost estimate.
No heat or no cooling at all - air may blow unheated, or nothing may blow - is often a control or power interruption rather than a dead furnace or air conditioner. Thermostat settings and batteries, a tripped breaker, a furnace switch left off after filter changes, a tripped safety, or an ignitor or pilot that will not light can all produce a silent house. So can a genuinely failed blower, control board, or compressor, but those come after the free checks. Work in order from the thermostat to the breaker to the unit switch, and note exactly what happens when you call for heat or cool: silence, a hum, clicking, or air at the wrong temperature each point somewhere different.
In mild weather this can wait for a normal appointment. It becomes urgent in deep cold, when pipes can freeze in an unheated house, and in extreme heat for infants, older adults, and anyone medically vulnerable. Any gas smell, carbon monoxide alarm, or scorch marks at the furnace makes it an emergency regardless of temperature - leave and call the utility or emergency services. A silent system with a CO alarm sounding is never a wait-and-see.
The most common cause. The thermostat is on the wrong mode, set above or below the wrong threshold, holding a schedule override, or its batteries have died so the call for heat or cool never reaches the system. Heat pumps add confusion with auxiliary heat settings. Always prove the thermostat is actually asking before condemning the equipment it controls.
Furnaces and air handlers sit on dedicated breakers and often a wall switch near the unit that looks like a light switch. Either gets bumped off during other work and forgotten. A tripped breaker that re-trips immediately is different - that signals a fault in the system and should not be repeatedly reset.
Older furnaces rely on a pilot; newer ones use an electronic ignitor that glows to light the burners. When ignition fails, the furnace may try, click, and shut down for safety, blowing unheated air briefly or nothing at all. A pilot that will not stay lit usually means its safety sensor has failed, not your technique.
Furnaces protect themselves: an overheated heat exchanger, a blocked vent, or a failed rollout or limit switch shuts the system down. Blower motors and control boards also fail outright, producing silence or a hum with no airflow. These are internal faults - the system is stopped by design or by failure, and internal diagnosis is technician work.
| Job size | Typical estimate (CAD) |
|---|---|
| Simple fix — the straightforward version of this repair | $120–$400 |
| Major job — complex, hidden, or replacement-level work | $450–$2,500 |
Estimates only, calibrated to Greater Toronto Area trade rates and adjusted by region on this site — not a quote. Your exact price depends on the cause, parts, and access. A personalized diagnosis narrows this range using your specific symptom.
Thermostat settings and batteries, breaker and furnace-switch checks, filter inspection, and a careful listen-and-log are the homeowner tier - they solve a real share of no-heat and no-cool calls for free. Everything inside the cabinet is a licensed HVAC technician job: ignition, gas valves, burners, refrigerant, control boards, and safeties. Call promptly in temperature extremes, and call emergency help first for any gas smell or CO alarm. A system that cycles and fails repeatedly should stay off until seen, to avoid compounding the fault.
Partly - the air handler works, but the heating or cooling stage is not firing. For heat, that points to ignition, gas supply, or a safety lockout; for cooling, to the outdoor unit, its breaker, or refrigerant problems the indoor unit cannot fix. Note whether the outdoor unit runs during cooling calls, and give that detail to the technician.
Short cycling like that commonly means the furnace is overheating and its limit safety is stopping it - often from restricted airflow such as a very dirty filter or closed registers - or a flame sensor is losing the burner signal. Try a clean filter and open registers once; if cycling persists, switch it off and book a technician rather than letting it hammer itself.
Many furnace labels print relight instructions, and standing pilots on older units are designed for it. But a pilot that repeatedly goes out, any gas smell, or any uncertainty about the steps means stop and call the utility or a technician. Modern furnaces with electronic ignition have no pilot to relight - repeated failed ignition is a fault to diagnose, not a button to keep pressing.
In deep cold, an unheated house can risk frozen pipes within a day or less depending on insulation and how cold it gets, especially on exterior walls. Keep interior doors open, open cabinets on exterior-wall plumbing, and let a vulnerable tap drip if heat will be out overnight in a freeze. Tell the HVAC company it is a no-heat call in cold weather - they prioritise those.
Describe what's actually happening and get a personalized diagnosis — DIY vs. call-a-pro verdict, real cost estimate, and top-rated local pros.