Your boiler is having trouble communicating with the internal clock or plug-in timer, preventing it from knowing when to turn on.

Programmer input

What causes this fault?

This fault happens when the boiler's main control board loses touch with the plug-in timer or external programmer responsible for scheduling your heating. It is usually caused by a loose connection in the internal wiring or a mechanical failure within the clock component itself, meaning the boiler doesn't receive the 'on' signal it expects. While the boiler's hardware might be fine, it stays idle because it can no longer see your heating schedule.