BoilerFaultCodesYour boiler has lost communication with its internal electronic controls or a safety switch has triggered to prevent overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like Fault 12 / 171 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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