A5 High

Worcester Bosch A5 Fault Code

The Worcester Bosch A5 fault code means: your boiler's temperature sensor responsible for monitoring stored hot water has developed a fault, preventing it from reading the temperature correctly.. It appears on 12 Worcester Bosch models 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: Heat store NTC sensor 2 defective

What causes the Worcester Bosch A5 fault?

This fault occurs when the electrical resistance in the sensor used to monitor your hot water storage reaches an impossible value, suggesting the component has failed internally. It is usually caused by natural wear and tear of the sensor's delicate internal elements or, occasionally, a loose connection in the wiring harness that links the sensor to the main control board.

Typical repair cost £90-160 (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 A5 fault code

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

Source

Worcester Bosch A5 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 31 August 2026