Hello
Thanks for the comments VCW 25 id open flued not sure of the vintage, but will look for a date code on the expansion vessel when I try to mend it,
I've opened the control box and manually tweaked the micro switches and the hot water comes on. So I think I that changing the diverter...
Got an old boiler, CH works, DHW does not work.
Suspect it could be divertor valve- I have manual but no mention of this - I think it called the 'water section'. So probably new valve or diaphragm
Also possible problem with flow switch have adjusted actuator for the two microswitches -this...