F26
Saunier Duval
Gas Valve Regulation / Modulation Fault
Boiler displays F26 and will not ignite
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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 gas valve modulation coil, Wiring fault to gas valve, Incorrect gas valve calibration, PCB output fault
How to Fix / Troubleshooting
Safety first: Isolate gas and power. Gas valve diagnostics must be done by a qualified engineer.
Engineer-level checks:
- Measure modulation signal from PCB to gas valve during operation.
- Check coil resistance and continuity.
- Verify burner pressure and adjust according to Saunier Duval data.
- Replace gas valve if modulation is not responding correctly.
Warning: Do not attempt to adjust or replace the gas valve without proper qualifications.
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Repair Difficulty
Professional Required
5/5
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