No heat right now: the complete 10-minute emergency checklist

Cold house, cold night. Run this exact order — it is arranged by how often each step is the answer, and every step is free.

1. Thermostat

Heat mode. Setpoint 5+ degrees above room temp. Fresh batteries. Screen alive.

2. Furnace switch

The light switch on or beside the furnace. On.

3. Breaker

Furnace breaker on; reset once if tripped.

4. Filter

If you cannot see light through it, swap it. Overheat shutdowns from clogged filters are the #1 no-heat cause in midwinter.

5. Blower door

Firmly seated. The door switch kills everything silently.

6. Gas

Valve handle parallel to pipe. Stove works? Then supply is fine.

7. Vents outside (high-efficiency)

Snow or ice blocking the PVC intake/exhaust is THE classic cold-snap failure. Clear both pipes.

8. Power-cycle

Furnace switch off, count 60 seconds, on. Clears many latched faults.

9. Read the blink code

Burners still not lighting? Watch the little window on the furnace for the flashing LED and count the pattern — then look it up on this site to know exactly what to tell the technician.

10. Space heaters + dripping taps

While you wait for the tech: heat the occupied room only, and on a hard-freeze night let faucets on exterior walls drip so pipes survive.

Safety line: Gas smell at any step: out of the house, utility emergency line, from outside. Below-freezing night with no fix in sight: burst pipes cost more than any emergency service call — do not toughing-it-out your plumbing into failure.

Is the furnace flashing a light?

If the burners will not light, the control board is almost certainly flashing a diagnostic code behind the little window. Count the flashes and look the code up by brand here — walking into the phone call knowing the code saves diagnostic time.

Step 9, by brand: what the code will probably say

On a no-heat night, the single most common thing the blink code reports is ignition lockout: the furnace tried to light several times, failed each time, and shut itself down on a timer. Every control family has this code, and knowing yours before you dial is the point of step 9:

Brand	Code	What it reports
Armstrong / AirEase / Concord / Ducane	5 flashes	Watchguard — burner failed to light, retries or recycles exceeded
Carrier / Bryant	Status code 14	Ignition lockout
Goodman / Amana	1 flash	Lockout after too many failed ignition attempts
Lennox	Alert code 270	Flame failed to ignite — Watchguard
Rheem / Ruud condensing	4 blinks	Lockout after five failed ignition attempts
Trane / American Standard	2 flashes	System lockout — retries or recycles exceeded
York / Luxaire / Coleman	7 red flashes	One hour lockout after ignition retries

The lockout timers explain a pattern that fools people: York's lockout releases after an hour and Carrier's after three, so a locked-out furnace delivers one burst of heat every hour or few and seems to "sometimes work". It is not recovering — it is failing identically on a schedule. If your heat has come in rare bursts all evening, you already know roughly what the code will say.

Fix it yourself, or call?

The ten steps above are the homeowner's whole share of this job — free, reversible, and worth doing before any call. Past them, be conservative: an ignition lockout means gas reached burners that did not light it, and the parts that decide whether it lights — igniter, flame sensor, gas pressure, gas valve, grounding — are all technician work on a combustion appliance. Do not keep power-cycling to force more attempts; each attempt delivers more gas.

What the call-out typically costs

Budget from the repair cost guide: the diagnostic visit is $75–150 and usually credited if you approve the repair, and after-hours emergency work adds $100–200 — the real cost of a midnight call versus a next-morning one. The two most common no-heat fixes are also the two cheapest: flame sensor cleaning at $80–200, and a hot surface igniter at $150–350 installed per the igniter cost page. If the house will hold above freezing overnight, morning rates are usually the right money call; if pipes are at risk, they are not.

First cold day of the season, furnace idle since spring? That failure set has its own page: furnace won't turn on after summer.

Error codes behind this symptom

If your furnace is flashing a code while doing this, these code families are the usual suspects: igniter fault codes, power supply codes, gas valve codes. Look your exact code up from the brand index, and see the furnace repair cost guide for what the fix typically runs.

Sources

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.