Furnace Repair from a Licensed Silicon Valley HVAC Contractor
The most common no-heat call we get is a failed hot surface igniter. The HSI is a brittle silicon carbide or silicon nitride element that glows red-hot to ignite the gas. They fail typically every 5-7 years from thermal stress and physical brittleness — they can crack just from being touched. We carry the 5 most common HSI part numbers (Norton 271N, White-Rodgers 767A, Robertshaw 41-401, Carrier LH33ZS001, and the universal 24V replacements) on every truck, so a failed igniter is usually a 30-minute fix.
The second-most-common repair is flame sensor cleaning or replacement. The flame sensor is a small rod that proves the gas has actually ignited; if it doesn't see flame, the gas valve closes for safety. Bay Area air carries enough particulates that the sensor accumulates a thin oxide film that prevents proper microamp readings. Cleaning with steel wool restores function in maybe 60% of cases; the rest need replacement. Either way, $200-$380 typical.
Inducer motor failures are also common, especially on Goodman, Amana, and Rheem 80% AFUE units 10+ years old. The inducer pulls combustion gases through the heat exchanger and pushes them out the flue. When the bearings dry out or the motor windings fail, the pressure switch never closes and the furnace won't fire. We diagnose with a manometer reading at the inducer pressure tap. Replacement runs $350-$800 for an OEM-equivalent.
Less common but more serious: cracked heat exchangers. We test for CO leaks with a Bacharach Fyrite InTech combustion analyzer on every gas furnace repair. A cracked heat exchanger allows combustion products (including CO) to mix with the supply air and circulate through your home — potentially fatal. We use a borescope to inspect heat exchanger tubes when symptoms suggest cracking (yellow flame, soot, CO alarm activation, occupant headaches). A bad heat exchanger usually means furnace replacement, not repair, since the heat exchanger is the most expensive component.
Other repairs we handle: gas valve diagnostics and replacement (always done with proper leak testing), draft inducer pressure switch replacement, control board diagnostics on Carrier Infinity / Trane TruComfort / Lennox iComfort smart systems, blower motor and capacitor replacement, thermocouple replacement on older standing-pilot units, and condensate trap cleaning on 95% AFUE condensing furnaces (algae blockage is common in our climate).
What's Included in Every Furnace Repair Job
- Same-day dispatch within 35 miles of Palo Alto
- 24/7 emergency service with typical 1-2 hour response
- Combustion analysis with CO testing on every gas furnace job
- Borescope heat exchanger inspection when symptoms warrant
- OEM parts where available; warrantied OEM-equivalent alternatives clearly disclosed
- Gas leak testing after every gas-side repair
- Diagnostic fee waived when repair is approved
- 1-year labor warranty on every repair
- Photo and reading documentation included
Common Furnace Repair Issues We Resolve
Furnace won't turn on / no heat
Cause: Failed hot surface igniter, dirty flame sensor, bad inducer motor, low gas pressure, control board failure
Fix: Sequential diagnostics — typical $180-$650 depending on root cause
Furnace short-cycling
Cause: Dirty flame sensor (most common), failing limit switch, oversized furnace, restricted airflow, draft issue
Fix: Flame sensor service, limit testing, airflow check — typical $200-$450
Yellow or sooty flame
Cause: Insufficient combustion air, blocked flue, dirty burners, cracked heat exchanger
Fix: Combustion analysis to determine cause; could be simple cleaning or could indicate replacement-grade safety issue
Loud or rumbling startup
Cause: Delayed ignition from low gas pressure or dirty burners, debris in burner box
Fix: Burner cleaning, gas pressure adjustment — typical $200-$420
Cold air from vents during heat call
Cause: Furnace lockout from failed sensor, blower running but burners not firing, reversing valve issue (heat pumps)
Fix: Sequential diagnostic — varies
Carbon monoxide alarm activation
Cause: Cracked heat exchanger, blocked flue, backdrafting, improper combustion
Fix: IMMEDIATE shutdown, ventilation, and combustion analysis. Often indicates replacement need.
Furnace runs but house is cold
Cause: Undersized equipment, duct leaks, blocked filter, bad blower wheel, low BTU input from gas pressure issue
Fix: Combustion + airflow + ductwork diagnosis
Our Furnace Repair Process
Emergency Dispatch
Call our 24/7 line and we have a tech on the way — typical response 1-2 hours during business, 1-3 hours after-hours.
Safety + Diagnostic
Combustion analysis, CO testing, gas pressure verification, electrical sequence test. Identifies the failure quickly.
Approved Repair
Flat-rate written quote presented before any work. Approved repairs use OEM-spec parts from the truck or sourced same-day from local supply.
Verification
Multiple cycle test, final combustion analysis showing safe CO levels, gas leak test on any gas-side work, walkthrough.
Furnace Repair Pricing in the Bay Area
Typical furnace repair pricing in our Silicon Valley service area runs $149 – $1 500 per repair. Most jobs complete in 1-3 hours for most repairs.
Every quote is flat-rate and provided in writing before work begins. Diagnostic fees are waived when repair is approved. We never use time-and-materials billing surprise pricing.
Local Context: Furnace Repair in Silicon Valley
Bay Area winters peak in the 30s-40s°F overnight in inland cities (San Jose, Sunnyvale) and 40s-50s°F overnight in coastal cities. Heating demand is moderate compared to colder climates but real — especially in the East Bay hills, the Santa Cruz mountains foothills (Los Gatos, Saratoga), and at higher elevations like Hillsborough and Portola Valley. Many Eichler homes in Palo Alto, Mountain View, and Sunnyvale use radiant slab heating rather than forced-air; we service the boilers and zone valves on those systems separately. California is also pushing heat pump conversion aggressively — federal IRA 25C credits ($2,000) plus TECH Clean California rebates ($1,000-$3,000) plus PG&E and CCA incentives can offset 30-50% of conversion cost.
HVAC Brands We Service for Furnace Repair
Furnace Repair FAQ
My furnace is making a clicking noise but no heat — what's wrong?
Almost certainly a failed hot surface igniter or a flame sensor that's not proving flame. The clicking is the gas valve trying to open and the safety system locking it back out. We typically resolve this same-day with a $200-$380 igniter or flame sensor service.
How fast can you get out for a no-heat call in Bay Area winter?
During business hours (8 AM – 8 PM), we typically dispatch within 1-2 hours to Palo Alto, Menlo Park, Mountain View, Sunnyvale, San Jose, and Cupertino. After-hours emergency response runs 1-3 hours. We prioritize homes with infants, elderly residents, or medical equipment.
My CO alarm went off — should I keep using the furnace?
No. Shut down the furnace immediately at the disconnect or thermostat, ventilate the home, and call us. CO alarm activation is a possible indicator of a cracked heat exchanger or blocked flue — both serious safety hazards. We respond to CO alarm calls within 1 hour with a Bacharach combustion analyzer and a borescope.
Should I repair my old furnace or replace it?
A useful framework: if your furnace is over 15 years old AND the repair is over $600, replacement is usually the better economic decision — federal IRA 25C credit covers up to $600 of furnace replacement, and a 95% AFUE unit will save 15-20% on gas vs an 80% AFUE. Heat pump conversion may be even better — eligible for $2,000 federal credit + $1,000-$3,000 TECH Clean rebate.
Do you do carbon monoxide testing as part of repair?
Yes, on every gas furnace job — included free. We use a Bacharach Fyrite InTech analyzer to measure CO ppm at the supply registers, in the flue, and at the burner. Safe target is under 9 ppm in living space; over 35 ppm is shutdown territory. We document the readings on your invoice.
Why does my furnace turn on then off after 30 seconds?
Short-cycling is most often caused by a dirty flame sensor — easy fix, $180-$280. Other causes: limit switch tripping from restricted airflow (clogged filter), oversized furnace cycling on overshoot, or thermostat short-cycling. Diagnostic is fast.
Can you service older gravity or atmospheric furnaces?
Yes. We service 80% AFUE atmospheric vent furnaces (B-vent), induced-draft 80% units, and 95-98% AFUE condensing furnaces (PVC vent). Older gravity furnaces (no blower fan) are essentially obsolete — most need replacement. We can diagnose and repair where possible, but parts availability is limited.
Do you handle propane furnaces?
Yes. Propane is common in unincorporated San Mateo County areas like Woodside, Portola Valley, and the rural parts of Half Moon Bay. We service propane gas valves, regulators, and verify proper LP conversion on units that came factory natural-gas configured.