Your boiler has detected an issue with how it mixes fuel and air for combustion, meaning it cannot operate safely or efficiently.

Error in regulating combustion – possible error with the calibration values chimney gas valve and board.

What causes this fault?

This fault occurs when the boiler's internal computer loses the ability to correctly balance the ratio of gas and air needed for a clean flame. It is usually triggered by a communication failure between the main control board and the gas valve, or because the internal sensors have detected that the combustion quality has drifted outside of safe limits.