how can i fix my worcester bosch greenstar 25si?

worcester greenstar 25 Si
GCN 47-311-84
installation manual
page 32
filling system
if the pressure keeps rising when filling key removed then we have to look at other possibilities of where cold mains water & CH water can meet
the first thing i would ask you is there an external filling still connected on the system somewhere
if it is connected i would check to see if the valves are passing
if the valves are passing just remove filling pipe & isolate valves
if no external filling loop on system then we would be looking inside the boiler
the most likely culprit would be the PHX plate heat exchanger
if you're really unlucky it could be the HYD hydroblock
i would test PHX & HYD by isolating cold mains supply to boiler & checking for any rise in pressure
if no rise in pressure problem lies in PHX/HYD
if rise in pressure problem lies in external filling loop

manwithnoname
April 2012