High
251 on Worcester Bosch Greenstar 1000

Your boiler's internal computer has detected a serious communication failure during its safety check, preventing it from starting up safely.

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.

What the manual says

Manufacturer manual

Flash test error

Shared across the Greenstar 1000 range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

Memory test failure

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

224View →227View →

All 106 fault codes on the Greenstar 1000

Seeing a different code? Every code this model can display, in one place.

2002012022032042082132142222232242272282292322332342352372382402412452492502522532542582592622632652682692702732752832842853053063413473513533573583603623633643655226041010101310181019102110231025106810731074208529082910291529162920292329242925292629272928293029312940294629482949295029512952295529562957295829592960296129622963296429652966296729722973297429802981

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