BoilerFaultCodesTechnical description
Main burner fails to light and pilot is extinguished when pressure on the control knob is released - Loose thermocouple connection into control valve.
What causes this fault?
This fault occurs when the boiler's safety mechanism fails to detect a steady flame, causing it to shut off the gas supply for safety. The most common reason is a worn-out or loose thermocouple sensor that can no longer send a signal to the gas valve, or a blocked pilot light burner that is too weak to heat the sensor properly.
This issue often surfaces during the first cold spell of autumn when the boiler is switched back on after being idle over the summer, as debris can settle in the pilot assembly.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.