Your boiler has experienced a safety lockout and has shut itself down to prevent damage.

Internal fault (locked-out)

What causes this fault?

This fault occurs when the boiler’s control board detects a safety issue or a failure to ignite, leading it to shut down the system for protection. The most common reasons include a worn ignition electrode that can no longer spark correctly or an internal electrical failure within the main circuit board. In some cases, a faulty sensor may be sending incorrect temperature readings, causing the boiler to trip its safety limit.