Changing taps – hot water?

Apologies for thick question!
I need to change my bathroom taps. Obviously I need to turn off the main stopcock but I have an unvented cylinder for hot water and I’m not sure if I need to isolate this too? The hot taps seem to retain some pressure even after the main stopcock is closed.
There is this sort of thing on top of the cylinder, and another tap like thing on one of the other supply pipes that can be closed.
Not flooding the house is obviously the aim…
Thanks in advance!

Close the valves

The hot taps seem to retain some pressure even after the main stopcock is closed.

Correct, if the HW tank is higher than the tap, gravity will drain the HW tank even if the mains is off.

Great – thanks.

Have you not got valves/ taps in the wall under the sink? Just turn them off.

Haven’t looked! They’re behind the bath at the moment but it’s freestanding so I’ll definitely check!

No!

if the HW tank is higher than the tap, gravity will drain the HW tank even if the mains is off.

Will it?

Is it not like a straw where nothing will come out it the vacuum is maintained (i.e. finger over the straw/feed to the tank switched off)?

[Although the answer is still yes, turn off the valves]

Edit: just actually thought about it…. Air could get in through the overflow!

No

So how are the taps on your bath connected to the mains water supply?

Flexible pipes connected straight to respective hot and cold supply, no separate valves.

Flexible pipes connected straight to respective hot and cold supply, no separate valves

I would take the opportunity to add isolation valves in, I’ve now added those to all the taps in the house, so changing tap inserts etc is much easier.

+1 on inline isolation valves

and for the cold water to the toilet cistern

And a little tip from a friend of mine who is a plumber….turn the valves off and on again at least once a year to make sure they don’t jam.

There is this sort of thing on top of the cylinder,

close this one, 90 degree turn.

Leave the other one alone, it’s likely the balancing valve for the DHW coil.

Don’t add local isolators to a bath filler. They’re a)not necessary and b) flow restrictive. If you really must, make sure they are full bore ones.

All sorted and no flooding occurred. I really can’t see the point of adding extra isolation valves – just another thing to go wrong / leak.

+1 on inline isolation valves

+2 – they are also useful for controlling water flow to taps. We have high water pressure so the cold tap in our en-suite, when turned fully on, will shoot water straight back out of the basin. With isolation valves we can partially close the cold one so the flow rate is lowered and we don’t constantly wet ourselves.