F09 error code, water heater not heating, may indicate line voltage or power supply issue

Safety first: Turn OFF power at the breaker. Use a properly rated multimeter if you are qualified.

Power checks:

• Verify the water heater is on a dedicated circuit with the correct breaker size per the rating plate.
• Remove the junction box cover on top of the heater and inspect wire nuts and ground connections. Tighten any loose connections.
• Measure supply voltage at the heater input (e.g., 240V for many electric models). Compare to the rating plate.
• Check for signs of overheating or discoloration at the wiring terminals.

Corrective actions:

• Correct any wiring errors (e.g., loose neutral, reversed hot/neutral on 120V hybrid models) according to Whirlpool wiring diagram.
• If supply voltage is correct and wiring is sound but F09 persists, the internal power supply on the control board is likely defective and the board should be replaced.

Warning: If you are not comfortable working with 120/240V circuits, contact a licensed electrician or technician.