Low
-Ii- on Worcester Bosch Greenstar 42CDi

Your boiler is performing a routine automatic safety check to fill its internal drainage system following a power cut or restart.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

The boiler runs for 15 minutes at minimum heating output to fill the condensate trap, the display (K) alternates between “-Ii-” and the central heating flow temperature. This occurs every time the mains supply has been interrupted.

From this model's manual
Verified against the Worcester Bosch Greenstar Si Combi I System Combi installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Wait 15 minutes for the cycle to complete automaticallyEnsure your thermostat is calling for heat during this timeDo nothing else; the boiler will return to normal operation on its own

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