Boiler shows A18, burner output limited, possible modulation issues
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.
Possible Causes
How to Fix / Troubleshooting
Critical safety: Do not attempt to adjust or dismantle the gas valve yourself. Only qualified gas technicians may work on gas components.
User checks:
- Observe operation: If the boiler only runs at minimum or maximum power and cannot modulate, note any associated noises or errors.
- Power cycle: Turn the boiler off and on to see if the fault clears temporarily.
Technician tasks: A professional must check gas valve modulation voltage, verify gas type and settings, and replace the gas valve or PCB if necessary. Combustion must be checked with a flue gas analyser after any gas work.
Repair Difficulty
Required Part
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