F9 error; heater may start but then shut down, especially at low flow rates.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Defective gas valve modulating coil, Blocked gas valve inlet filter, Incorrect gas type setting, Faulty control board output to gas valve

Safety: Gas valve work must be done by licensed personnel. Limit DIY to visual checks.

Check gas type: Confirm the heater is set and jetted for the correct gas (natural gas vs LPG) as per rating plate.
Visual inspection: Look for signs of overheating or burning on the gas valve and its connector.
Stable gas supply: Ensure other gas appliances do not cause large pressure drops when starting.
Professional calibration: If F9 persists, a technician must measure gas pressures and adjust or replace the gas valve.

Professional Required 5/5

Gas Valve Assembly

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