Switching Hot water off in mains pressure system

[taycast]

A down stairs hot tap drips so needs fixed. I think I can fix this but dont know how to switch the hot water off as cant see a tap leading from the tank. The salesman that sold me the house said it had a mains pressure hot water system with a big red expansion tank next to the hot water tank. If I switch the cold mains off, will this stop the pressure in the hot system? Surely I will be flooded with all the water above me from the first floor pipes, and tank when I take the tap to bits?

I am also worried that if I manage to get it fixed, how do I repressurise the hot water system?

 

[flameport]

Turning off the cold will also do the hot - the cylinder is fed by the cold mains water supply.

The water in the pipes will drain out, the cylinder will not, as the outlet is at the top.
You won't be flooded with any water, since you would obviously be opening the hot tap to drain out any water before dismantling it.

When finished, just turn on the cold supply again.

If there is a service valve below the hot tap, you don't need to do any of that - just turn off below the hot tap.

 

[taycast]

Ah thats why the cylinder doesn't drain. Just so I get my head round this, it is the mains cold pressure that forces the hot out of the top of the tank? So when I switch cold back on, I will have a bit of air in my hot taps, alleviated by opening them till water reappears? That should be it?

 

[flameport]

That is it.