Low
4-A2 on Worcester Bosch Greenstar 2000

Your boiler is performing a routine initial setup or maintenance check to fill the internal condensate trap with water and is not actually at fault.

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

Siphon filling program: 0: switched off, 1: switched on with minimum power, 2: switched on with minimum heat output. The ++ symbol and flow temperature appear alternately in the display.

From this model's manual
Verified against the Worcester Bosch Greenstar 27cdi 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 approximately 15 minutes for the program to complete automaticallyEnsure your thermostat is calling for heat to allow the boiler to cycle through the processIf the code persists for over 30 minutes, restart the boiler by pressing the reset button

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