Your boiler is struggling to control its flame correctly and has shut down as a safety precaution.

Unable to regulate combustion – possible calibration value issue, chimney gas valve or board.

What causes this fault?

This fault occurs when the boiler's internal computer can no longer accurately manage the mix of gas and air needed for a steady flame. It is usually triggered because the electronic control board is receiving incorrect readings or the gas valve has lost its ability to regulate the flow precisely. The system shuts down entirely because it cannot guarantee the boiler is burning fuel safely or efficiently.