Fault 12 / 170 High

Worcester Bosch Fault 12 / 170 Fault Code

Also written as FAULT12170 — same fault.

The Worcester Bosch Fault 12 / 170 fault code means: your boiler's internal computer has lost communication with a central safety component or an external controller, causing the system to shut down for safety.. It appears on 1 Worcester Bosch model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 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 the Worcester Bosch Fault 12 / 170 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.

Typical repair cost £120-£350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the Fault 12 / 170 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch Fault 12 / 170 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026