F.26
Vaillant
Gas Valve Fault / Regulation Error
Boiler displays F.26, no ignition, fan may run briefly
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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 actuator, Loose gas valve wiring, Incorrect gas valve calibration, Faulty main PCB driving gas valve
How to Fix / Troubleshooting
Safety: Gas valve work must only be carried out by a Gas Safe registered engineer. Do not attempt to adjust or replace the gas valve yourself.
- Reset boiler: Try a single reset. If F.26 persists, leave the boiler off.
- Check supply: Ensure the gas isolation valve is open and that other gas appliances work. If there is a supply issue, contact your gas supplier.
- Engineer actions (for reference): A technician will check the gas valve coil resistance, wiring harness, and PCB outputs, and may recalibrate or replace the gas valve and/or PCB as per Vaillant procedures.
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Repair Difficulty
Professional Required
5/5
Required Part
Gas Valve Assembly
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