all u need to do is shut of the cold water. download the worcester manual go down to section changing parts and its all there gl. i even put in the website and its page 24 section 17.
https://www.heatingspares247.com/download/Boiler_Manuals/Worcester/28I_Discontinued_Nov_05_Installation_And_Servicing_Instructions.pdf
kash
December 2012