Your boiler has detected an issue with its internal combustion levels and cannot regulate the gas flame safely.

Current values reached – check combustion values and CO2 calibration, try resetting the boiler if this fails. Either the board or the valve will need replacing.

What causes this fault?

This fault occurs when the boiler's internal sensors detect that the gas and air mixture is no longer burning within safe, controlled limits. It usually happens because the gas valve is failing to regulate the flow correctly or the main control board has lost the ability to calibrate the flame, leading the system to shut down for safety.