Why did my furnace stop working suddenly?
A furnace that stops without warning has usually shut itself down on purpose — a safety switch tripped, the control board locked out after repeated failed ignition attempts, or something cut power. That's the furnace protecting itself, so the fix is finding what it reacted to rather than simply resetting it.
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What you can safely check
- Thermostat
- Blank screen points at power or batteries rather than the furnace itself.
- Breaker and furnace switch
- Reset the breaker once and confirm the service switch near the furnace is on.
- Filter
- A badly blocked filter trips the high limit and the furnace stops until it cools.
- Outside vents
- On a high-efficiency furnace, snow or ice over the exterior intake or exhaust will stop it dead. A genuinely common New Brunswick cause.
What’s probably going on
- Ignition lockout
- After three or four failed attempts the board locks out and waits, rather than continuing to try.
- Tripped limit switch
- Overheating from restricted airflow. Resetting without fixing airflow just repeats it.
- Condensate safety switch
- A full pan or blocked drain cuts the furnace deliberately.
- Pressure switch or blocked vent
- The furnace won't fire unless it can prove the vent is clear.
Stop here and call
If resetting the breaker gets you one cycle and then it quits again, stop resetting it. The repeat is the diagnosis, and repeated lockout cycles are hard on the equipment.
What we do about it
We pull the fault history off the control board — it records why it shut down — and fix that cause rather than clearing the code and leaving.
Still stuck?
Tell us what the system is doing and we’ll tell you what it takes to fix — free quotes, no obligation, and a straight answer about whether it’s worth repairing.