Your boiler's internal control board cannot safely operate the gas valve, preventing the system from firing up for heating or hot water.

Relay gas valve defect

What causes this fault?

This fault occurs when the boiler's main control board detects a hardware failure in the electrical relay that controls the gas supply. It is essentially a safety conflict where the board can no longer reliably open or close the gas valve, forcing the system to shut down to prevent potential safety risks. The root cause is typically a component failure on the circuit board itself or a communication error between the board and the gas valve.