Your boiler is having trouble synchronizing its clock with other connected parts of your heating system.

What causes this fault?

This fault happens when there is a breakdown in communication between the boiler and other smart controllers or expansion modules connected via the LON network. It is usually caused by an incorrect setting in the boiler's menu or a conflict in how the devices are trying to synchronize their internal clocks. In most cases, it is a configuration error rather than a physical part failure.