Before and after
A Taylorsville customer called us at 11 AM on a December weekday morning after their furnace stopped producing heat overnight. House temperature had dropped to 60°F by morning. The 8-year-old condensing furnace was attempting to ignite but failing — the customer could hear it cycling through ignition attempts without successfully starting. This case study documents a diagnostic that traced the failure through the pressure switch back to a blocked condensate drain.
Customer Situation
- Home: 2015-built Taylorsville two-story, approximately 2,400 sq ft
- Existing equipment: 8-year-old Trane 96% AFUE two-stage condensing furnace
- Symptom: Furnace cycling through ignition attempts without successful firing; no heat output
- Severity: Cold but not severe (28°F outdoor, 60°F indoor)
- Time of call: 11:00 AM weekday
Diagnostic Approach
Arrival: 12:50 PM (under 2-hour same-day response)
Initial observations: – Inducer motor starting on thermostat call – Pressure switch failing to close (verified with multimeter) – HSI not energizing because pressure switch open – Error code on control board: “open pressure switch”
Diagnostic measurements: – Inducer motor amp draw: 1.0 amps (nameplate 1.2) ✓ – Pressure switch hose: connected, no obstruction visible – Pressure switch operating threshold tested: 1.2″ wc (manufacturer spec: closes at 1.0″, opens at 0.6″) – Actual inducer pressure: 0.7″ wc (below switch closing threshold)
Why inducer pressure was low:
Checked condensate drainage: – Condensate drain line: visible water backup at drain trap – Drain line obstruction: blockage approximately 18″ downstream of trap – Result: water backing up into inducer housing area, reducing effective draft pressure – Pressure switch correctly preventing operation under reduced draft conditions (safety system working as designed)
Root Cause and Repair
Root cause: Blocked condensate drain line caused water backup, reducing inducer pressure below switch closing threshold. Safety system correctly prevented ignition.
Repair performed:
- Cleared blockage from condensate drain line (used pressure flush)
- Inspected drain trap and cleaned biological growth
- Verified drain flow
- Replaced condensate neutralizer media (overdue maintenance)
- Restarted furnace
- Verified all measurements within specifications after restart
Combustion analysis after restart: – CO: 11 ppm ✓ – O2: 7.8% ✓ – Combustion efficiency: 95.2% ✓ – Pressure switch closing properly – Temperature rise: 43°F ✓
Final Cost
Customer’s invoice: – Diagnostic visit: $99 (applied to repair) – Drain line clearance: $185 – Neutralizer media replacement: $75 – Labor: $145 – Total: $504
No equipment damage — furnace returned to full operation. Customer enrolled in maintenance plan ($189 annual) which includes annual condensate system service.
Customer Outcome
Equipment restored by 2:30 PM same day. Customer’s home temperature reached 68°F by 5 PM. Subsequent operation reliable.
Maintenance plan tune-up the following spring caught: – Condensate neutralizer needing replacement (replaced) – Filter loading (filter replaced) – Minor combustion adjustment for optimal efficiency – All findings documented in service report
What This Case Study Demonstrates
- Symptom (no heat) traced to root cause (blocked drain) through systematic diagnostic
- Safety system working correctly — pressure switch prevented unsafe operation
- What we didn’t do: Replace pressure switch unnecessarily; recommend equipment replacement; bypass safety controls
- Maintenance prevents recurrence — annual condensate service catches drain issues before they cause failures
Need Furnace Repair?
If your furnace has stopped producing heat in Taylorsville, call (385) 250-0687.
- Phone: (385) 250-0687
- Address: 4454 Manhattan Ct, West Valley City, UT 84120
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