John Rumm explained :
The quick look I gave it appeared to suggest that. What I am not sure of is
how you would set the various parameters without also having some kind of
controller in there... What timer/programmer have you currently got?

Just a basic electronic one, with battery backup, with an override
until next action, on for one hour when off on both CH and HW.

If it will work, the intelligence for setting it has to be in the
boiler itself, so it must signal the HW demand back to the boiler, via
the ebus. The boiler does have ebus terminals. It also has terminals
for the NTC outdoor sensor - Do you happen to know whether the NTC is a
10K or 100K?

The manual for the boiler is here -
https://www.vaillant.co.uk/downloads...ual-876622.pdf

It has rather a lot of settings in there, monitoring options and fault
codes. Unfortunately I cannot find any mention of suitable extra
controls and options at all. As you suggested, there is no 'big
picture'.