was going to check CH, and the ****ing clock is bust. It was the cheapest possible option for the Vaillant boiler (notice I say option, reading the manual the base boiler comes with nothing).
Anyway, since I have been meaning to install a programmable stat so we can "advance" the heating when needed, and from the hall not having to go to the utility and have a week/weekend pattern set up, this looks like the right time.
Anyone suggest stat that would do the job. Ideally it would replace the existing wired stat ?
Cheers all - and seriously, thanks Geoff. Good call.