On / Off (CH fault) Medium

Worcester Bosch On / Off (CH fault) Fault Code

Also written as ONOFFCHFAULT — same fault.

The Worcester Bosch On / Off (CH fault) fault code means: your boiler is failing to switch on for heating even though your hot water is working perfectly fine.. It appears on 1 Worcester Bosch model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Boiler not operating during central heating demand (HW ok). Check: Live demand at ST10-LR, Facia mounted timer, CH knob in winter position, Diverter valve, Control board.
Typical repair cost £150-350 (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 On / Off (CH fault) fault code

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

Source

Worcester Bosch On / Off (CH fault) 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