Furnace Not Turning On
No heat at all is one of the more urgent HVAC problems — here's what's usually behind it.
Worth checking first — a thermostat with dead batteries or set incorrectly can look exactly like a furnace failure.
Furnaces run on electrical power even for gas systems (to run the blower and ignition) — a tripped breaker will stop it cold.
Older systems with a pilot light that's gone out, or newer systems with a failed electronic ignitor, won't fire even though everything else looks normal.
Many furnaces have a safety switch that shuts the system down if airflow is too restricted — a severely clogged filter can trigger this.
If the gas valve is closed or there's a supply issue, the furnace won't ignite even if everything else is functioning.
Leave the house immediately, don't operate any switches or the thermostat, and call your gas utility from outside. Contact us after the gas company has confirmed it's safe.
Frequently asked questions
If it's cold and you have no heat, it's urgent — but not typically dangerous on its own. If you smell gas, that's different: leave the house and call your gas utility immediately, then us.
Thermostat batteries and settings, and whether the breaker for your furnace has tripped. If both check out, it's time for a professional diagnosis.
See our full Furnace Repair service or browse other common symptoms.
The first-cold-night sequence — what to try, then what we test
Before calling, run the free checks: thermostat actually on heat and set above room temperature (worth saying — it resolves real calls), breaker on, furnace switch (looks like a light switch near the unit) on, filter not suffocated, and gas supply on if other gas appliances work. If those pass and it still won't fire, the usual suspects are our territory: a dust-fouled flame sensor (the county's most common first-cold-night failure — the furnace lights, can't confirm flame, and shuts itself down safely), a cracked or aged ignitor, a failed control board, or a gas valve issue. Safety line: any gas smell means leave first and call the gas company from outside — before us, before anything. Everything else, we diagnose with the panel off and the evidence shown.