Gas Furnace Short-Cycling After 3 Seconds in Spring Trails Pflugerville - Flame Rectification

Anita_R_SpringTrails Homeowner

Posted in Pflugerville Homeowner Forum • Travis County

Question: When the heat turns on in our Spring Trails house, the furnace burners light up with blue flames, stay on for exactly 3 to 4 seconds, and then shut off completely. The draft inducer fan continues spinning and it retries 3 times before locking out. What is causing this rapid shutdown?

✓ VERIFIED PRACTIONER DIAGNOSIS

Cody_R_TDLR_Tech Texas TDLR Class A Master Tech

Texas Department of Licensing & Regulation Certified

Microscopic silica and carbon oxidation on the flame sensor rod dropped microamp direct current below the control board 0.5 microamp detection threshold, triggering safe lockout.

Diagnostic Procedure & Field Restoration:

Hot surface igniter energized and gas valve opened with normal manifold pressure (3.5 in. w.c. natural gas).
In-line microamp meter measured 0.18 microamps DC between flame sensor and integrated control board (minimum required: 0.8 microamps).
Removed flame sensor rod and burnished the metal surface using ultra-fine non-abrasive Scotch-Brite cloth (avoiding steel wool).
Reinstalled sensor rod; signal jumped to 3.8 microamps DC and furnace completed full 45-minute heating cycle smoothly.

Experiencing this exact symptom in Pflugerville?

Technicians carry exact replacement capacitors, contactors, and diagnostic test instruments on service trucks for rapid same-day restoration.

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