Furnace Not Heating

high priority

Furnace runs but house stays cold

Understanding This Problem

A furnace that runs without providing heat is a common winter complaint. The cause could be simple or indicate a more serious issue requiring professional attention.

Quick Answer

Furnace Not Heating usually points to thermostat set incorrectly, clogged air filter, pilot light or ignition failure. Start with the safe checks listed below, document what changed, and stop running the equipment if the symptom involves burning smells, gas odor, repeated breaker trips, ice, water damage, or unsafe operation.

Common Causes

Thermostat set incorrectly

Clogged air filter

Pilot light or ignition failure

Gas supply issue

Blower motor problems

Heat exchanger issues

Blocked flue or venting

What You Can Do

Verify thermostat is set to HEAT mode

Check and replace filter

Verify gas supply valve is open

Check pilot light or ignition

Schedule professional inspection

What to Document Before Scheduling

When furnace not heating started and whether it happens during heating, cooling, startup, shutdown, or long cycles.

Thermostat setting, actual room temperature, filter condition, breaker status, and any error codes.

Photos or short videos of the thermostat, indoor unit, outdoor unit, vents, leaks, ice, or unusual sounds.

System age, brand, model number, recent maintenance, and any previous repair recommendations.

Prevention Tips

Schedule fall furnace tune-up
Replace filters before heating season
Test furnace before cold weather arrives

Questions Before Approving Repair

Which finding best explains furnace not heating, and what reading or observation supports it?

Can any safe homeowner step be tried first, or should the equipment stay off until inspection?

What is the difference between the immediate repair, follow-up maintenance, and replacement planning?

What parts, labor, exclusions, warranty assumptions, and safety risks should be written into the scope?

High Priority

This issue should be addressed promptly to avoid damage or discomfort.

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Services That Can Help

Furnace Repair

Expert furnace diagnostics and repair.

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Furnace Tune-Up

Pre-season furnace maintenance and safety check.

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Related Heating Issues

Furnace Not Turning On

high

Furnace won't start at all

Furnace Short Cycling

medium

Furnace turns on and off too frequently

No Heat From Vents

medium

Some or all vents blow cold air when furnace is running

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We serve homeowners throughout the Bay Area experiencing this issue:

Menlo Park Palo Alto Atherton Redwood City San Carlos Belmont San Mateo Foster City Burlingame Hillsborough Woodside Portola Valley

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