Furnace Repair in Salt Lake County

January 7, 2024. The retired Yalecrest schoolteacher Margaret R. you read about on our heating services page — the one who got a $11,400 replacement quote from a national franchise for what turned out to be a $245 igniter swap. Her case represents a pattern we see roughly two or three times per winter month: a competing contractor sends a tech who’s been on the job 8-18 months, the tech doesn’t actually diagnose, and the recommendation defaults to full system replacement because that’s where the franchise’s commission structure points. The economic incentive runs against the homeowner. Our incentive structure is different: our techs are W-2 employees on hourly pay (no commission), the diagnostic fee is the same whether the repair is $245 or $1,840, and we keep customers for 12-18 years on average because we don’t sell them equipment they don’t need. Furnace repair done right means measuring with instruments, explaining what the measurements show, and quoting the actual fix. Below is what that looks like in detail.

Most furnace failures fall into one of nine categories. We’ve ordered them by approximate frequency across hundreds of winter calls per year on the Wasatch Front. Each category has a typical diagnostic procedure, a typical repair cost, and a typical timeline. The single exception — the failure mode where repair almost never wins economically — is heat exchanger cracking, which we borescope-inspect on every diagnostic visit for equipment older than 10 years because operating a cracked heat exchanger creates a carbon monoxide hazard. For broader context on heating, see the heating services hub; for replacement economics see the furnace installation page.

The Nine Most Common Furnace Failure Modes

1. Hot Surface Igniter Failure (~22% of Calls)

The hot surface igniter (HSI) is a ceramic element that heats to approximately 2,400°F to ignite the gas. Modern silicon nitride igniters last 5-8 years typical; older silicon carbide igniters last 3-5 years. Symptoms: furnace cycles through ignition attempts (typically 3 attempts before lockout), no flame visible at burners, board lockout code indicates failed ignition.

Diagnostic: Visual inspection of igniter for visible cracks. Ohmmeter resistance test (silicon nitride: 40-90 ohms; silicon carbide: 50-400 ohms; open circuit = failed). Voltage at igniter terminals during ignition attempt.

Cost: $185-$285 installed depending on equipment access and OEM vs. universal replacement.

2. Flame Sensor Fouling (~18%)

The flame sensor is a thin metal rod inserted into the flame path that detects flame presence via flame rectification. Carbon and oxidation deposits accumulate on the rod over months of operation, eventually reducing the microamp signal below the threshold the board recognizes. Symptoms: furnace ignites successfully then shuts down within 3-7 seconds; board logs flame-loss error.

Diagnostic: Microamp measurement at flame sensor terminal during operation. Healthy: 2-6 µA. Failing: under 1.0 µA. Visual inspection shows white/black coating on the rod.

Cost: $145-$195 for cleaning (preferred when sensor is structurally sound) or $185-$285 for replacement (when sensor is corroded or bent).

3. Inducer Motor Failure (~15%)

The induced-draft motor pulls combustion gas through the heat exchanger and out the vent. Bearings wear out, capacitors fail, windings short. Symptoms: failure to start (pressure switch never closes because inducer can’t create vacuum), excessive noise from inducer area, intermittent operation. On condensing furnaces, also responsible for condensate evacuation.

Diagnostic: Listen for bearing noise. Measure motor amperage against nameplate FLA. Capacitor microfarad check (PSC motors). Pressure-switch closure test (does pressure switch close when inducer runs).

Cost: $485-$840 installed depending on motor size and equipment access.

4. Pressure Switch Failure (~10%)

Pressure switches detect inducer draft and prove that combustion gas is being properly exhausted before the gas valve opens. Switches can fail in either direction: failing closed (unsafe, allows gas valve to open without proper draft) or failing open (system won’t start because board doesn’t see required draft signal). Most failures are open-circuit due to age or contamination.

Diagnostic: Manometer measurement of actual draft pressure during inducer operation. Continuity test of pressure switch contacts during simulated draft. Tube inspection for blockage from condensate, spider webs, or debris.

Cost: $285-$385 installed.

5. Gas Valve Failure (~8%)

The gas valve opens to deliver gas to the burners when the control board signals demand. Valves fail from age, contamination from gas line debris, electrical solenoid failure, or pilot light valve issues (on older equipment). Symptoms: no gas flow to burners on ignition attempt, complete failure to fire even with successful igniter operation.

Diagnostic: Voltage measurement at gas valve terminals during ignition attempt (should see 24V on demand). Gas pressure measurement at outlet of valve during operation (should see manifold pressure spec, typically 3.5″ WC at sea level or 2.4-2.9″ WC altitude-derated). Inlet pressure measurement (should see Dominion Energy’s 7″ WC supply pressure under load).

Cost: $485-$840 installed depending on valve type (single-stage, two-stage, modulating). Modulating gas valves on premium equipment may run $840-$1,200.

6. Control Board Failure (~7%)

The integrated furnace control board manages ignition sequence, blower operation, safety circuits, and diagnostic codes. Boards fail from voltage spikes (lightning during summer monsoon storms, utility transients), internal capacitor failure, water damage from condensate overflow, or simply aging electronics. Symptoms vary by failed function: complete no-power, intermittent operation, blower running continuously without thermostat call, error code lockouts.

Diagnostic: Voltage measurement at board outputs against expected values. Error code interrogation on equipment with diagnostic displays. Visual inspection for swollen capacitors or scorched components.

Cost: $385-$640 installed for standard residential boards. Modulating-condensing equipment boards (Carrier Infinity, Trane ComfortLink II, Lennox iComfort S30, Bryant Evolution Connex) typically $540-$960 due to more complex control logic.

7. Blower Motor Failure (~8%)

Indoor blower motor delivers heated air through the supply ducts. Failure modes: bearing failure (squealing, progressive over weeks), winding short (motor runs hot, trips on internal thermal protector), capacitor-related failure on PSC motors. ECM variable-speed motor failures usually present as control board faults or speed control issues rather than mechanical failure.

Diagnostic: Visual inspection for visible damage. Bearing noise listening during operation. Motor amperage compared to nameplate FLA. Capacitor microfarad measurement (PSC motors). For ECM motors: manufacturer-specific diagnostic tools.

Cost: $485-$920 installed for PSC motor replacement. $640-$1,440 for ECM variable-speed motor replacement.

8. Limit Switch Trip from Airflow Restriction (~7%)

The high-limit switch shuts down the burners if the heat exchanger or supply plenum gets too hot, typically because airflow has dropped due to filter restriction, ductwork blockage, or blower failure. Symptoms: furnace fires briefly then shuts down, restarts after 5-10 minute cooldown, repeats indefinitely without producing useful heat. Equipment is functioning correctly — it’s protecting itself from overheat damage. The actual problem is upstream airflow restriction.

Diagnostic: Inspect filter, return air grilles, supply ducts. Measure static pressure across the air handler. Test blower motor amperage. Limit switch continuity test.

Cost: Typically not a limit switch issue per se — cost is whatever the upstream problem is. Filter replacement and return air cleaning: $145-$245. Blower motor service: $485-$920.

9. Heat Exchanger Cracking (~5% of Calls, but Highest Priority)

The heat exchanger separates combustion gases from the air delivered to the house. Heat exchanger cracks or pinholes allow combustion gases (including carbon monoxide) into the supply air stream — a potentially fatal safety issue. Cracking is caused by metal fatigue from thermal cycling, soot buildup from improper combustion (especially on equipment installed without altitude derate), or overheat damage from chronic airflow restriction. Risk increases with equipment age, particularly after 12-15 years.

Diagnostic: Borescope inspection of heat exchanger interior (we use the Inspection Camera 4 with 10mm scope on every furnace older than 10 years during diagnostic visits). Combustion analysis comparing CO readings during cold-start to hot-cycle (rising CO indicates cracking). Visual inspection of flame characteristics (yellow tipping or flame waver indicates heat exchanger issues).

Cost: Heat exchanger replacement on residential furnaces is typically $1,800-$3,400 in parts and labor on equipment that’s still made. On most equipment 12+ years old, the heat exchanger replacement cost approaches 40-65% of full furnace replacement cost, which makes replacement the better economic choice. Full furnace replacement scenarios on the furnace installation page.

Our Furnace Diagnostic Process

1. Initial conversation. What’s happening, when did it start, any unusual sounds, smells, or behavior changes. Recent service history if available.
2. Visual inspection. Outdoor venting condition, indoor equipment exterior, gas supply piping, electrical connections, condensate drain (on condensing equipment).
3. Power-on sequence observation. Watch the full ignition sequence: thermostat call, inducer startup, pressure switch closure, igniter glow, gas valve open, burner ignition, blower delay startup, sustained operation, blower-off delay, system shutdown.
4. Combustion analysis. Testo 320 combustion analyzer measurement during steady-state operation. Records CO (air-free, must be under 100 ppm), O₂ (target 6-10%), CO₂ (target 8-11%), flue gas temperature, draft pressure (target -0.05″ to -0.10″ WC for natural-draft equipment).
5. Gas pressure measurement. Manometer at inlet of gas valve (should see 7″ WC Dominion Energy supply under operating load). Manometer at manifold (should see altitude-derated spec for the equipment).
6. Static pressure measurement. Pitot tube measurement across the air handler (total external static pressure should be at or below manufacturer max, typically 0.50″ WC).
7. Heat exchanger borescope inspection. Required on every diagnostic visit for equipment older than 10 years. Visual inspection of heat exchanger interior tubes for cracking, pinholes, soot accumulation, or perforation. Photo documentation.
8. Carbon monoxide ambient test. CO meter reading in equipment room (must be under 9 ppm baseline) and in occupied spaces (must be under 9 ppm). Elevated readings indicate venting failure or heat exchanger compromise.
9. Findings explained and written quote. All measurements documented. Findings explained to homeowner with the actual numbers vs. spec. Repair scope and cost itemized. Customer signs authorization before work begins.
10. Repair and verification. Repair performed. System cycled through full operation. Combustion analysis re-run to verify proper post-repair operation. Documentation completed.

Pricing Reference (Q2 2026)

Diagnostic visit (weekday business hours):

$89, credited toward authorized repair the same visit

Diagnostic visit (after-hours / weekend / holiday):

$149, credited toward authorized repair the same visit. Waived for Comfort Care plan members.

Common furnace repairs (parts and labor installed):

• Hot surface igniter replacement: $185-$285
• Flame sensor cleaning: $145-$195
• Flame sensor replacement: $185-$285
• Inducer motor replacement: $485-$840
• Pressure switch replacement: $285-$385
• Gas valve replacement (single/two-stage): $485-$840
• Gas valve replacement (modulating): $840-$1,200
• Control board replacement (standard): $385-$640
• Control board replacement (modulating-condensing): $540-$960
• Blower motor replacement (PSC): $485-$920
• Blower motor replacement (ECM): $640-$1,440
• Limit switch replacement: $245-$385
• Capacitor replacement (PSC blower or inducer): $185-$285
• Flame rollout switch reset and inspection: $145-$245
• Condensate trap cleaning (condensing equipment): $145-$245
• Drain line clearing (condensing equipment): $145-$245
• Heat exchanger replacement (when economically justified): $1,800-$3,400 — usually points to full furnace replacement instead

Comfort Care plan member discount:

15% off parts and labor on any repair. After-hours dispatch fee waived. Priority dispatch on emergency calls.

Emergency vs. Routine Repair

Emergency dispatch (24/7) is available for situations where waiting could create a safety or property risk:

• No heat with indoor temperature below 50°F
• Suspected gas leak (smell of mercaptan additive, sulfurous odor, or hissing from gas line)
• Carbon monoxide alarm sounding in the home
• Visible smoke or burning smell from furnace
• Water leak from condensing furnace creating active property damage
• Electrical arcing or repeated breaker trips at the furnace disconnect

Routine repair calls (system not heating optimally but no immediate safety concern) are typically scheduled within 24-48 hours during business hours. Comfort Care plan members receive priority scheduling.

Frequently Asked Questions

How fast can you get to my house for furnace repair?

Emergency dispatch (no heat below 50°F, gas leak, CO alarm) typically arrives within 90 minutes during business hours, 2 hours overnight or weekends. Routine repair calls are scheduled within 24-48 hours during business hours. Comfort Care plan members receive priority scheduling and typically get same-day or next-day appointments.

Do I have to pay the diagnostic fee if I authorize the repair?

No. The diagnostic fee ($89 weekdays, $149 after-hours) is credited toward authorized repair when you proceed with the work the same visit. If the diagnosis shows the problem is outside our scope (e.g., a gas service issue requiring Dominion Energy, or a chimney issue requiring a chimney specialist), the fee covers the time spent diagnosing and recommending the appropriate trade.

Should I replace my furnace if the heat exchanger is cracked?

Almost always yes. Operating a cracked heat exchanger creates a potentially fatal carbon monoxide risk — combustion gases mix with the supply air being delivered into your home. Heat exchanger replacement parts are typically $800-$1,400 plus 4-6 hours of labor ($600-$1,200), totaling $1,800-$3,400 installed. On equipment 12+ years old, that cost is 40-65% of full replacement, which doesn’t make sense vs. a new furnace with full new manufacturer warranty. We never recommend operating a cracked heat exchanger; we always recommend either heat exchanger replacement (on newer equipment with warranty) or full furnace replacement (on older equipment). The case for full replacement is on the furnace installation page.

Why does my furnace cycle on and off so much?

Most common cause: oversized equipment. A furnace sized at 100,000 BTU/hr input when the home only needs 50,000 BTU/hr will heat the air rapidly, trip the high-limit switch or thermostat satisfaction, and cycle off. After cooldown it cycles back on, repeating every 6-12 minutes throughout heating operation. Other causes: failing limit switch, undersized return air, dirty filter, blower motor speed mismatch. Our diagnostic measures static pressure and verifies cycling pattern against expected behavior. The fix depends on root cause — sometimes a $145 filter and return air repair; sometimes (in cases of oversized equipment) full system right-sizing.

What if I don’t want to replace my furnace but the heat exchanger is cracked?

You don’t have to replace it — you simply can’t operate it. We will disable the equipment (shut off gas supply at the meter or at the equipment shutoff valve), red-tag it as unsafe per IFGC requirements, and notify you in writing. Operating a known-cracked heat exchanger creates liability for the homeowner (and for any contractor who continues to service it). If full replacement isn’t financially viable, talk to us about the financing options on the financing page or about HEAT Inc. emergency replacement programs via the community involvement page.

Schedule Furnace Repair

For emergency dispatch, call the 24/7 line. For routine repair, schedule online or call during business hours.

• Emergency Line (24/7): (385) 300-1867
• Address: 756 E Winchester St #322, Salt Lake City, UT 84107
• Email: info@saltlakecityheatingairconditioning.xyz
• Utah DOPL HVAC Contractor License: #11567823-5501
• EPA Section 608 Universal (Lead Tech): #608U-2009-447129

Schedule Repair →

Office Hours

• Emergency Service: 24 hours a day, 7 days a week
• Office Staff: Monday – Friday, 8:00 AM – 5:00 PM
• Closed: Weekends and State/Federal Holidays (emergency line always active)