What does F66 mean?
Heater relay on the control board has failed or is stuck.
Common causes
- Failed relay on control board
- Shorted heating element
- Overloaded circuit
- Control board failure
Diagnostic & testing steps
- 1. Test heating element resistance: 15-30 ohms
- 2. Check for shorts to ground on heater circuit
- 3. Inspect control board relay for signs of overheating
- 4. Measure incoming voltage: 240VAC
- 5. Replace control board if relay is stuck or burned
Tools required
- Multimeter
- Phillips screwdriver
- Torx screwdriver
OEM parts & part numbers
Main Control Board (EPWL)
Part numbers: 7781593, 9384072
Safety warning
⚠️ Turn off breaker before inspecting heater circuit. Fire risk if relay stuck closed.
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