Your boiler has lost its settings and doesn't know how to burn gas efficiently, so it has shut down as a safety precaution.

Calibration request – boiler has detected an absence of calibration control.

What causes this fault?

This fault occurs when the boiler's internal computer suffers a memory failure and loses the specific tuning data required to manage the burner. The most common reason is an electronic glitch in the main control board or a communication failure between the board and the gas valve, meaning the boiler no longer knows how to safely mix gas and air.