Sub-Zero Furnace: Not Working at All
Usually a failed igniter, a dirty flame sensor, a tripped limit switch, or a thermostat issue. Add a photo of your Sub-Zero Furnace in the box below: the Triage Profile says what it is, how urgent it is, and who to call.
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In the next five minutes
Safe first steps, before the call. Nothing here needs a tool.
If you smell gas, a carbon monoxide alarm sounds, or anyone feels dizzy or sick: don’t touch any switch or plug, leave and get everyone out, then call 911 or the gas company from outside.
No gas smell? Switch the furnace off at the thermostat and at its breaker.
Don’t use it again until it’s checked, and keep people away from it.
Everything else about this problem
Is it an emergency?
Is a Sub-Zero furnace that isn't working an emergency?
Usually not, but it can be. Because this can be an emergency, leave it off and get it checked; don't reset it or turn it back on. Stop and call a pro if it smells like burning, trips the breaker again, or runs on gas and you smell gas.
Symptoms & causes
No heat output whatsoever, and the thermostat display might be blank or unresponsive. There are no fan sounds, pilot light indications, or error codes displayed on the unit itself.
Tools & parts
A multimeter is essential for checking electrical continuity and voltage at various components. You will also need a screwdriver set and potentially a wire stripper for accessing and testing connections.
Safety first
Always shut off the main power to the furnace at the circuit breaker before beginning any inspection or repair work. Ensure the gas supply valve is closed if you suspect a gas leak or are working near gas lines.
When to call a pro
If you are uncomfortable working with high voltage electricity or gas lines, call a certified HVAC technician immediately. Complex control board failures, gas valve issues, or persistent ignition problems often require specialized testing tools and expertise.
Related problems
More Sub-Zero furnace problems
Check another symptom for your Sub-Zero Furnace.
Not working: other brands
Guides and hubs
A resident sent you this?
What a property manager should do when a resident reports no heat: the first message, how urgent, who to send.
The manager’s checklist →Ask AI about this problem
What it is, how urgent, who to call
Add a photo of your Sub-Zero Furnace in the box at the top. The Triage Profile says what it is, how urgent it is, and who to call.