Dave - thanks for the reply.

With the system all switched on - ie heating and hot water - turning down the cylinder stat (you should hear it click) while the room one is higher
than ambient temp should force the motorised valve to the heating position, and you should hear this happening.

ok - here is my steps:

1) set the boiler program to be for both HW and CH
2) boiler comes on
3) turn down the thermostat on the cylinder - i hear that "click"
4) boiler turns OFF

Room one - you mean any room in the flat? well all the room are pretty
cold (since no CH is coming on!)

after step 4), then thats it for me - nothing else seems to happen.

why would having room one higher than ambient temp 'force' the
motorised valve to the heating position?

wouldnt that happen when the room temp is lower than my room thermostat
settings? i.e. LOWER than ambient temp?

They're normally wired for hot water priority, so if both stats are
calling for heat, the water one wins.

'They' as in the valve right?

so can i unscrew the screws on the valve and take off the cream plastic
casing to look inside without killing myself?

So if the hot water works, this means (please confirm someone)

a) Water pump is working
b) Valve is working for hot water

correct? Should the water pump and the valve making some
noise/vibration when everything is working? its hard to tell from mine
- when boiler comes on, the pump does seem to be vibrating and so does
the valve - but its so little vibration, i'm not sure if it is the
boiler's vibration filtering on to them (since they are so close to
each other) ?

thanks
Kiichi