When is a problem with furnace urgent?
Treat a furnace problem as urgent when it creates an immediate safety exposure, active damage, loss of an essential service in dangerous weather, or rapid worsening.
What this means
Furnace covers heat production, ignition, cycling, sounds, and odours. Relevant observations include Runs but blows cold air, Will not start, Starts and stops quickly, Makes a new loud noise, Smells like gas or rotten eggs. The correct response depends on age, design, climate, usage, installation, recent work, and the exact manufacturer instructions; these observations narrow next steps but do not prove a failed part.
Safe checks
- Identify active water, heat, smoke, odour, arcing, movement, sewage, structural change, or loss of essential service.
- Move people away and use only a normal safe shutoff or disconnect when accessible.
- Call emergency services for immediate danger; otherwise contact the relevant qualified trade.
Stop and get help if
- Leave for a gas odour or carbon-monoxide alarm; stop for smoke, scorching, damaged wiring, or repeated breaker trips.
- Do not open combustion, refrigerant, high-voltage, or sealed compartments.
Which professional to call
Use a qualified HVAC technician when the condition exceeds safe user access or the visible checks do not explain it.
Find the relevant tradeSource and method
This answer combines HomeSOS's structured triage with safety boundaries supported by a public source. It does not replace inspection.
Health Canada: Home safetyReviewed August 12, 2026