Every time your thermostat calls for heat, the furnace runs a fixed checklist. The inducer motor starts and proves draft by closing a pressure switch, the hot surface igniter heats up, the gas valve opens, the burners light, and the flame sensor confirms there is fire. Only after all of that does the blower begin sending warm air into the house. Finding the step that fails is most of the job. Around San Francisco, CA, the usual failure points are a flame sensor fouled with oxide, an igniter cracked by years of heating and cooling, a pressure switch that stays open because of a weak inducer or a clogged condensate trap on a high-efficiency unit, and control boards with burned relays. Each one halts the startup, and from the hallway they all look alike.
San Francisco HVAC repairs furnaces by testing the sequence, not guessing at it. Our experienced technicians verify each stage with a meter rather than a hunch: igniter resistance, flame signal in microamps, pressure switch operation against actual inducer draft, gas valve voltage, and blower and capacitor health. Every visit includes the safety fundamentals on a fuel-burning appliance: the heat exchanger inspected, connections leak-tested, and draft confirmed, because the difference between a furnace problem and a furnace hazard is not visible from the thermostat. We measure temperature rise against the data plate before we leave so the fire and the airflow are matched the way the manufacturer intended.
Conventional or condensing, gas, propane, or electric, we work on them all, across every major brand, including the traps, drains, and dual pressure switches that come with high-efficiency models. The parts most likely to fail are already stocked on the truck: igniters, flame sensors, pressure switches, capacitors, inducer assemblies, and blower motors. That is why most repairs are finished in a single trip. If your furnace is down anywhere in San Francisco, call (415) 234-5360 and we will get the burners lit today.
For air conditioning breakdowns, see AC Repair in San Francisco.
How Much Does Furnace Repair Cost in San Francisco?
For most San Francisco homes, a furnace repair runs $150 to $600. Cleaning a flame sensor is a small job; replacing a blower motor or control board is a bigger one. You'll get a written, upfront price from San Francisco HVAC after we diagnose the problem.
| Repair | Typical cost | What it usually means |
|---|---|---|
| Flame sensor cleaning or replacementFurnace lights, then shuts off within seconds | $80–$250 | Burners light but cut out almost immediately |
| Hot surface igniter replacementNo ignition; one of the most common winter failures | $150–$400 | Furnace clicks and tries to start but never lights |
| Draft inducer motorLoud humming or grinding at startup, then lockout | $400–$1,000 | Startup fan fails, furnace won't fire |
| Blower motorBurners run but little or no air comes out of the vents | $400–$1,500 | Burners run but little or no air comes out of the vents |
| Control boardFurnace won't respond to the thermostat | $300–$700 | Furnace won't respond to the thermostat |
| Gas valve replacementIgniter glows but gas never flows to the burners | $250–$700 | Valve fails to open, so the furnace never lights |
Typical ranges for common repairs. Your exact price is quoted after diagnosis.
What Moves the Cost Up or Down
- Furnace age and type, because 90%+ efficiency models have more specialized parts
- Whether a cracked heat exchanger is found, which usually means replacement rather than repair
- Timing, such as a no-heat call on a cold night versus a scheduled repair
- Access to the furnace in attics, closets, or crawlspaces
When a repair gets expensive on an aging furnace, you'll see both options before deciding. Call (415) 234-5360 for a quote.
When to Call for Furnace Repair in San Francisco
Spotting the early warning signs gives you the chance to act before the situation spirals into something far more expensive. Watch for these telltale signs that professional help is needed:
- Rust streaks, soot, or water around the cabinet or flue
- Flames that start, last a few seconds, and go out again and again
- The furnace clicks and glows but the burners never light
- The blower runs constantly but the air never warms
- A furnace that shuts off every few minutes before the house warms up
- Loud booms at startup caused by delayed ignition
- Grinding or high-pitched squeals from the blower
- A flame that burns soft and yellow rather than steady blue
Act Before It Gets Worse
What seems like a minor issue today can take out a compressor or heat exchanger tomorrow. If you notice any of these signs, contact San Francisco HVAC at (415) 234-5360 for a prompt inspection.
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Why Professional Furnace Repair Matters
Gas, open flame, high voltage, and a flue all share one cabinet in a furnace, and the most dangerous failure is the one you cannot see: a damaged heat exchanger that lets combustion gases into the air the blower circulates. Every morning that delayed ignition keeps booming at startup, that exchanger takes more stress. The diagnostic side has its own pitfalls. When a furnace trips its high limit, the switch itself may be bad, or the furnace may be protecting itself from a clogged filter or a failing blower. Replacing the switch when the real issue is airflow removes a safety device and leaves the actual problem in place.
At San Francisco HVAC, no symptom gets treated in isolation. A meter tells us the flame signal, so we never condemn a good sensor while the real culprit, a cracked igniter or a weak gas valve, stays in place. We confirm draft at both the pressure switch and the flue, measure temperature rise against the data plate to catch airflow problems early, and leak-test every gas connection with instruments, not a guess. When we are done, the furnace has proven itself safe and correct through a full cycle, and if it is nearing the end of its useful life, you will get an honest assessment.
What to Expect From Our Furnace Repair
Our systematic workflow delivers thorough, lasting results on every job. Here's how we handle furnace repair from start to finish:
Startup Sequence Testing
Instead of guessing, we follow the startup sequence step by step, with readings on the inducer, pressure switch, igniter, flame sensor, and gas valve, until the broken link is clear.
Combustion Safety Check
On every visit, we inspect the heat exchanger, leak-test the gas connections, and confirm the flue is drafting. A repair is not complete until the unit is proven safe.
Targeted Repair
Igniters, flame sensors, pressure switches, capacitors, and motors ride on the truck, so most furnaces are lit and heating again before we pack up.
Full Verification
The last step is a full-cycle test: temperature rise matched to the data plate, smooth ignition with no booming, and every limit switch and safety control confirmed working.
Furnace Repair Prevention Tips
Taking preventive measures can help you avoid costly heating and cooling problems down the road. Put these technician-approved steps to work around your property:
- Clear boxes, lint, and above all chlorine-based cleaners out of the furnace area
- Keep a working carbon monoxide alarm on every level of the home and check it each month
- Change the filter monthly during heating season; it is the cheapest furnace part you will ever buy
- On high-efficiency models, keep the condensate trap and drain line clear and draining
- Have the furnace checked every autumn, while a weak igniter or fouled sensor is still an easy fix
- Notice how the furnace sounds at startup, because a quiet light-off is healthy and a boom is not
- Make sure the furnace has clear combustion air; a packed utility room starves the burners
Comparing DIY and Professional Furnace Repair
Online tutorials may help in a pinch, yet lasting repairs and code-compliant installations usually depend on professional methods and trained technicians. Consider the following comparison:
| Factor | DIY Attempt | Professional Service |
|---|---|---|
| Exchanger Cracks | Damage hidden inside the cabinet | Checked every time we open the unit |
| Ignition Faults | Parts swapped against a code list | Each ignition component tested |
| Gas Connections | Small leaks missed entirely | Connections leak-tested with instruments |
| High-Limit Trips | Safety switch bypassed or swapped | Filter, blower, and ducts checked for the cause |
| Airflow Match | Blower speed left wherever it was | Blower tuned to the rated rise |
| Final Check | Declared fixed after one flame | Complete cycles tested before we leave |
Talk to a Furnace Repair Expert
The sooner you call, the sooner your comfort is back. Reach San Francisco HVAC for fast service.
Call (415) 234-5360 NowWhere We Provide Furnace Repair
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