BoilerFaultCodesYour boiler's internal computer has lost communication with a central safety component or an external controller, causing the system to shut down for safety.
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 a stable electrical connection with the safety sensors that monitor for overheating. It is usually caused by a loose wiring connection or a sensor that has permanently failed due to wear and tear. Because the boiler cannot verify that the water temperature is safe, it shuts down immediately to prevent damage.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like Fault 12 / 170 — 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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