Isolating water (mains unvented system)

[iwest]

hi there, I need to change a shower mixer (aqualisa hydramax/colt) in my daughters flat which is easy enough, however I just need an idea of how to isolate the hot/cold supplies so I can do it.
It is a 12 year old Barratt flat with hot water cylinder tank in the airing cupboard and expansion vessel so I guess it is mains pressure unvented. There is a gate valve in the airing cupboard in one of the smaller pipes coming out of the top of the hot cylinder but not a lot else as far as I remember. If I switch off the mains stopcock and that gate valve will it do it or will some draining be required? Thanks for your help!

 

[mrStat]

Probably be ok just shutting the stop cock - There will always be a bit of water come out... You sure the gate valve isn't the bypass for the heating system? Pictures always help... But if it is an unvented - Shut the stop cock; open the taps and let it vent. Swap the shower; close taps; open stock cock; check for leaks; yada yada yada.

 

[iwest]

Thanks Mrsat, job done, there were shower hot and cold gate valves on the airing cupboard but the hot was seized so had to turn off the main stopcock but job done, cheers buddy