This is almost certainly your problem. This valve should be
operated by your programmer. Make sure electrical power is
switched on to both and check fuses.

By which programmer though? the programmer underneath the boiler OR the
7 day immersion heater one? or both?

i do remember seeing a cable going into the valve from the boiler
programmer though.

when you electrical power to BOTH - you mean the boiler programmer AND
7 day immersion heater programmer right? if so, i see lights coming on
for both so power must be good??

Same when i use the taps/shower in the bath of MAIN bathroom
so it looks like the pump is only coming on for HOT water ONLY in the
main bathroom - why is this?

Being a flat it means the feed to the copper cylinder cannot be
mounted high enough to supply sufficient HW pressure. Cold water
comes through at mains pressure. So the pump boosts pressure for
the entire HW system while acting as a power shower.

but why does the shower pump come on for cold water in the en-suite
ONLY and not for the main bathroom then?

how can i reduce this noise? i read that i can have a box and some
insulating stuff around it - but also read this is not good because the
pump may overheat?

the pump is just sitting on a shelf inside the airing cupboard

Slide something padded under the pump. Foam, cardboard, rubber,
anything that reduces transmission of the pump's vibes.

kiichi
the shower pump is sitting on a wooden shelf and it has 4 pipes (i
think 4 but will check) coming in - if i slide something underneath the
shower pump, would that cause these pipes to break?

thanks!
kiichi