High
T4 on Worcester Bosch Junior 28i

Your boiler has failed an internal test of the component that switches water between your radiators and your taps, meaning your heating or hot water may not work correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Three way valve test

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

T1View →T6View →EAView →

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