E79 = blower / combustion fan failure. The control commands the blower to start; the hall sensor doesn\'t confirm expected RPM. Lockout for safety (no fan = unsafe combustion).
Diagnostic sequence
1. Listen for blower start
- On call for hot water, blower should spin up audibly before ignition
- Silent = motor not energized OR motor failed
- Whining/grinding = bearings worn
2. Blower power verification
- 120V at blower terminals during start (multimeter)
- No voltage = control board not commanding; may be control board fault
- Voltage present but no spin = motor or capacitor
3. Capacitor check (cheap first test)
- Many WGRGH blowers use a run capacitor (3-5 μF)
- Capacitor swells or fails = motor won\'t start
- Replace capacitor ($15-25); often fixes apparent motor failure
4. Hall sensor / tach signal
- Blower has hall sensor reporting RPM to control
- If motor spins but hall reports no signal = bad sensor or wiring
- Bad tach signal triggers E79 even with healthy motor
5. Vent obstruction
- Blocked PVC vent = high back-pressure = motor can\'t reach target RPM
- Inspect intake and exhaust terminations
Cost
- Capacitor: $15-25
- Blower motor (OEM): $200-400
- Hall sensor: $40-80 (sometimes integrated with motor)
- Contractor labor: $200-400
Bottom line
E79 = blower issue. Capacitor first (cheap test), then motor, then vent obstruction. Within 5-year parts warranty, Westinghouse ships replacement.