Isolate water to heating interface unit (HIU)

[Old UKPF 101119]

Hi there. I'm trying to work out how to isolate the water in my flat, so I can fix a leaking shower tap. My flat has a heating interface unit (HIU), which is being fed by various pipes - see photo. I'm not sure though what pipes I should / can isolate to stop the flow, can anyone provide any advice? Cold water is simple, there is a lever labelled for 'cold water isolation valve', which works fine. However, there's no equivalent for hot water, and I'm a bit worried about just turning them all off as there's quite a bit of pressure in the system. I can't find any valves on the pipes leading to the shower to isolate, so I need to do this centrally. Thanks for any advice.

 

[ShaunCorbs]

2nd from the left

Red tap label

Left to right

Cold water in
Hot water out
Main boiler flow in
Main boiler return out
Rads flow
Rads return

 

[Old UKPF 101119]

Thank you so much, worked perfectly.