809 High

Worcester Bosch 809 Fault Code

The Worcester Bosch 809 fault code means: your boiler has lost the ability to accurately measure the temperature of the water inside its internal store, which prevents it from heating your water correctly.. 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: A0 Thermal store sensor defective
Typical repair cost £150-250 (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 809 fault code

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

Source

Worcester Bosch 809 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 7 July 2026