BoilerFaultCodesTechnical description
System configuration: BUS device missing. HLC has tripped or is faulty.
What causes this fault?
This fault occurs when the boiler's main control board loses its connection to vital internal components or when a safety sensor detects that the water inside is getting too hot. The most common reason is a tripped High Limit Stat, which acts like a safety fuse to shut the system down if it senses a risk of overheating. In some cases, it can also be caused by loose internal wiring or a communication error within the electronic control unit.
This fault is slightly more common in winter when the heating system is running for long periods, which can cause older components to overheat or reveal underlying circulation issues.
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.