How much does it cost to fix Worcester Bosch error code 815 W/B?

Typical repair cost for the Worcester Bosch 815 W/B fault is £120-190 including labour.

815 W/B High

Worcester Bosch 815 W/B Fault Code

Q: What does the Worcester Bosch 815 W/B fault code mean?

Your boiler's temperature sensors are receiving conflicting or incorrect readings, causing the system to stop working correctly to protect itself.

Also written as 815WB — same fault.

The Worcester Bosch 815 W/B fault code means: your boiler's temperature sensors are receiving conflicting or incorrect readings, causing the system to stop working correctly to protect itself.. It appears on 10 Worcester Bosch models in our database.

Technical description: Low loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage

What causes the Worcester Bosch 815 W/B fault?

This fault occurs when the boiler's control system detects a discrepancy between the water temperature sensors, often because the sensor monitoring the external mixing point is giving an impossible reading. The most common reasons are a physical failure of the sensor itself, an electrical fault in the connecting wires, or the sensor being installed in the wrong location during a complex system setup.

Typical repair cost £120-190 (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 815 W/B fault code

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

Source

Worcester Bosch 815 W/B 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