What warning signs should I watch for around furnace?
Track changes in operation, sound, smell, moisture, temperature, movement, and visible condition around furnace; patterns matter more than one isolated observation.
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
- Compare furnace with a similar unaffected area or a documented normal cycle.
- Note whether these known observations appear: Runs but blows cold air, Will not start, Starts and stops quickly, Makes a new loud noise, Smells like gas or rotten eggs.
- Photograph and date visible changes from a safe position.
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