Tank not getting hot water

[SteveShaun]

Central heating working fine. Also the boiler keeps turning off and back on again constantly. please help.
Photos of my setup below.

On trying to increase pressure I did turn on of the valves, but I dont know which one, or what way.

Also under the valve at the bottom to the right of the tank you can see there is a tiny slow drip coming from underneath the valve.

 

[ShaunCorbs]

Could be a few things does the top pipe out the port valve get hot ?

Also the leaking gate valve just need the little brass nut on the body where the shaft comes out nipping up

 

[SteveShaun]

Could be a few things does the top pipe out the port valve get hot ?

Also the leaking gate valve just need the little brass nut on the body where the shaft comes out nipping up

It looks like that little yellow box constantly lights up "CH" not "HW" - I've got a nest system, but even when i press the big button next to the boiler that should activate both hw and ch only ch comes on.

to be clear, if i call for hw, ch comes on. if i call for both, only ch comes on.

 

[ShaunCorbs]

Sounds like either your nest isn't wired right / not working or you have a duff port valve

Has this only happen since you have had the nest installed??