Hi I'm new, i hope this is the right place to ask for boiler help

My MIL has a Vaillant VCW 242e, currently it won't provide central heating, it's working fine for hot water, the thermostat is sending the request for ch to the boiler, the fan and pump runs, but nothing else.
we've had a plumber out who so far i trust, and he's said its the hydro block, and there's no new parts available. is this the same item as a water valve? i've done a bit of searching and not found any reference of hydro block, maybe it's just his term for it? if so it has been dripping very slightly from here for a long time. it looks like if it is that i could replace it myself, but i'm not sure if there's any adjustmeant or setting up required. i've emailed Valient for the manuals, but if anyone has one that wouldn't mind emailing that would be great too.

Rick:

I'd like to think I know more than an average homeowner about hydronic heating systems, but I've never heard of a "hydro block".

If you don't get any other responses in here, register and post that same question in the boilers forum on this site:
Terry Love Plumbing & Remodel DIY Forum & Blog

Most of the people answering questions in there are plumbers, and it's much more likely they would have heard of such a thing and know what it does.