High
i21 on Worcester Bosch Greenstar Heatslave II

Your boiler is displaying its internal software version, which indicates a configuration error rather than a physical part failure.

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

Software version - HIS software version of the HIS PCB.

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

i20View →i22View →

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