Your boiler is struggling to send signals between its internal components because the communication line has a low electrical voltage.

Fault: eBUS - Undervoltage on the eBUS

What causes this fault?

This fault occurs when the boiler's internal communication system experiences a power drop that prevents components from 'talking' to each other. The most common reason is an electrical short circuit in the wiring or a failing electronic control board that can no longer maintain the correct voltage. It can also be triggered if external smart controls or thermostats are incorrectly wired into the boiler's data port.