Boiler displays F26; the burner does not ignite, though the fan may run.

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 modulation coil, Incorrect gas valve calibration, Wiring fault to the gas valve, PCB modulation output fault

Safety: Isolate the gas and power supply before any work on gas components. Only Gas Safe registered engineers may adjust or replace gas valves.

Reset and observe: If F26 appears consistently on ignition attempts, the gas valve or its control is suspect.
Engineer tasks:
- Check gas valve wiring and connectors.
- Measure the modulation coil resistance and compare it to the specification.
- Verify the correct gas valve type and configuration for the boiler.
- Replace the gas valve and/or PCB as indicated by diagnostic tests.

Do not attempt to adjust gas valve screws; incorrect settings can cause dangerous combustion.

Professional Required 5/5

Modulating Gas Valve

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