Emergency — No Heat

Furnace Not Turning On?
What to Check Before Calling

Your furnace won’t start — no heat, no fan, no response. Bay Area winters are mild but nighttime temps in the hills can drop into the 30s. Here’s what to check yourself before calling for furnace repair.

Smell gas?

Leave the house immediately. Call PG&E at 1-800-743-5000, then call us.

(408) 581–2241

Common Causes

Five issues account for the vast majority of “furnace won’t start” calls we respond to.

Thermostat Issue

Dead batteries, wrong mode (set to COOL instead of HEAT), or temperature set below room temp. Try fresh batteries and verify settings. Some smart thermostats lose Wi-Fi and revert to a schedule that doesn’t call for heat.

Tripped Breaker or Power Switch

Check the furnace breaker in the electrical panel. Also check the power switch on or near the furnace — it looks like a regular light switch and is easy to flip off accidentally. Gas furnaces still need electricity for the blower, ignitor, and control board.

Dirty Flame Sensor

The #1 cause of “furnace tries to start but shuts off after a few seconds.” The flame sensor is a small rod that detects whether gas is actually burning. When coated with carbon buildup, it can’t sense the flame and shuts off gas flow as a safety measure.

Failed Ignitor

Modern furnaces use a hot surface ignitor (HSI) instead of a pilot light. These glow orange to ignite gas. After 3–5 years of use, ignitors crack or weaken. Symptoms: you hear the inducer motor start, a click, but no ignition.

Clogged Air Filter

A severely clogged filter restricts airflow, causing the heat exchanger to overheat. The high-limit safety switch shuts the furnace down to prevent cracking. The furnace may try to restart several times then lock out completely.

Safe Checks You Can Perform

Check the thermostat. Set to HEAT, temperature above current room temp, fan on AUTO. Try fresh batteries. Turn off, wait 5 minutes, turn back on.

Check the furnace power switch. Look for a standard light switch on or near the furnace. Make sure it’s ON.

Check the breaker. Find the furnace breaker in your panel. If tripped, reset once. If it trips again, stop and call.

Check and replace the air filter. A clogged filter can cause safety lockout. Replace it even if it looks “okay” — it costs under $20 and eliminates a common cause.

Check the gas supply. Make sure the gas valve near the furnace is in the ON position (handle parallel to the pipe). Also verify other gas appliances work (stove, water heater) to confirm gas supply to the house.

Gas safety: If you smell gas (rotten egg odor), do NOT flip any switches, light matches, or use your phone inside the house. Leave immediately, call PG&E (1-800-743-5000) from outside, then call us.

Signs You Need a Professional

Furnace starts then shuts off after seconds — dirty flame sensor or failed ignitor. Both are common repairs ($150–$300).

Flashing error code on the furnace — most furnaces have a small LED that blinks a diagnostic code. Note the pattern (e.g., 3 blinks) and tell the technician — it speeds up diagnosis.

Inducer motor runs but no ignition — you hear a whooshing sound (inducer clearing the combustion chamber) but no flame. Failed ignitor or gas valve issue.

Any smell of gas — leave the house, call PG&E, then call us. Do not attempt to troubleshoot a gas leak yourself.

Why Choose North Breeze

Same-day service

NATE certified

All furnace brands

5.0 rated

Upfront pricing

Parts on truck

Related Services

Frequently Asked Questions

Why does my furnace click but not ignite?

The inducer motor runs, gas valve clicks open, but the ignitor doesn’t light the gas. Usually a cracked or worn hot surface ignitor — one of the most common furnace parts to fail. Replacement costs $150–$300 and takes about an hour.

How much does furnace repair cost?

Common repairs: ignitor ($150–$300), flame sensor cleaning ($100–$200), inducer motor ($300–$700), control board ($400–$800). We diagnose first and provide an upfront quote. Learn more about furnace repair.

Is a furnace that won’t start dangerous?

A furnace that simply won’t start is not dangerous — the safety systems are working as intended by preventing ignition. However, if you smell gas, that IS dangerous. Leave immediately and call PG&E. A CO detector alarm with a running furnace is also an emergency — evacuate and call 911.

Furnace Won’t Start?

Same-day furnace repair for Bay Area homeowners. We carry ignitors, flame sensors, and common parts on our truck.