Cabling for motorised valves

[ericmark]

but with vented, wouldn’t the water tank need to be higher than the top floor shower?

No. You can either pressurise the hot coil or you can use a power shower, either way tank not pressured, look at the diagram I put up.

 

[SJRSJR]

You can either pressurise the hot coil or you can use a power shower,

It’s too late to get power showers but please could you point me in the direction of pressurising the hot coil please? Everything I’ve read about vented cylinders says the tank has to be above all hot water outlets.Thanks

 

[flameport]

I don’t fancy the idea of an annual call out either (or pressurised boiling water flying about!)

Neither of those things happen.
If you really want it to be inspected annually, then it's done when the boiler is serviced for no or a tiny extra cost. Most people don't bother.

There is no boiling water, and it certainly doesn't 'fly about'. Stories you may have read about unvented cylinders exploding and so on are just that - stories made up by people with agendas, mainly those that want to sell you some pointless, expensive and complex alternative. Probably by the name of Gledhill or something similar.

The only example of an unvented cylinder exploding is a Mythbusters episode where they obtained one, deliberately removed all of the safety devices, welded all of the pipes and other outlets permanently closed and left it heating continuously via an electric element with no thermostat for hours. There are no circumstances where that could happen in any real installation.

direction of pressurising the hot coil please?

Don't go there.

The viable options are
unvented cylinder if the mains water supply is suitable or can be upgraded so that it is
or a vented cylinder and a pump if it isn't and can't be.

Unvented cylinders are not new or fangled, they have been used all over the world for decades. Standard equipment in most countries.
Unfortunately in Britain, ye old vented piece with a disgusting open cistern in the loft still persists, and plenty of people are convinced that some instant water heater combination boiler effort is the only alternative. It isn't.