Condition
Furnace No Heat – Fan Blowing
Blower runs but air is cold. Igniter, flame sensor, or gas valve issue.
Possible Causes
Cracked Furnace Igniter
Over time, the igniter becomes brittle and cracks, preventing the furnace from lighting.
Root Cause Analysis →Diagnostic Tests
- Visual inspection for cracks
- Ohm test
- Check for glow
Repair Options
Oxidized Flame Sensor
Soot buildup on the sensor causes it to lose its ability to detect the flame, shutting down the furnace.
Root Cause Analysis →Diagnostic Tests
- Inspect for oxidation
- Clean with steel wool
- Check microamp reading
Repair Options
Incorrect Thermostat Calibration
If the thermostat fails to sense the correct temperature, it won't signal the HVAC to run.
Root Cause Analysis →Diagnostic Tests
- Jump R to W
- Check 24V
- Verify heat mode selected
Repair Options