F13
Protherm Gas Valve Modulation / Control Fault

F13 displayed, appliance may run at reduced power or shut down

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Safety Warning

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.

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Possible Causes

Defective modulating gas valve coil, Broken modulation wiring, Incorrect gas valve calibration, Faulty control signal from PCB

How to Fix / Troubleshooting

Safety first: Turn off gas and power. Gas valve work must be done by licensed personnel.

  • Check wiring: Inspect the modulation coil connector and cable from the PCB to the gas valve for damage or loose contacts.
  • Measure coil resistance: With power off, measure the resistance of the modulation coil and compare with Protherm specifications. Replace the gas valve if out of range.
  • Verify control signal: A technician can measure the DC control voltage or current from the PCB during operation to confirm proper modulation.
  • Replace gas valve or PCB: If the coil is good but modulation signal is absent or erratic, replace the main PCB. If the coil is faulty, replace the complete gas valve assembly.

Warning: After gas valve replacement, a full combustion analysis and leak test are mandatory.

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Repair Difficulty

Professional Required 5/5

Required Part

Modulating Gas Valve
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