High
T4 on Worcester Bosch 30i Junior

Your boiler is having trouble switching between the heating and hot water functions because an internal valve is stuck or failing its startup check.

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

EAView →T1View →T6View →

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