Two questions if I could please?

1. Theres a capped 15mm pipe under my bath by the taps, opposite end to radiator. How can I tell if this is a mains cold supply, other than sawing the end off and squirting water everywhere? (Its slightly warm to touch when heating is on, may be near a heating pipe below the floor? Hence why asking)

2. Would the 22mm supply to the bath cold tap be direct or from a header tank?

Reason for asking these is I want to install an electric shower, I've heard its best to take the supply from mains rather than tank, but it would be easier to take it from the bath cold supply.

If you have a tank in the loft then it's gravity fed. If you've got a combi boiler (no tank in loft and no hot water cylinder) then it will be a direct mains feed.

1. No need for a soaking to find out!

you can always buy a 15mm pushfit end cap, turn of mains water, drain header tank, cut of cap end, get a mate to turn on mains and see if you get flow before pushing on the end cap to close of the pipe again. costs about 1 quid.

I was hoping there may be a simpler solution! Anyone else experience of fitting a shower and where to take the water supply from?

1. Theres a capped 15mm pipe under my bath by the taps, opposite end to radiator. How can I tell if this is a mains cold supply, other than sawing the end off and squirting water everywhere? (Its slightly warm to touch when heating is on, may be near a heating pipe below the floor? Hence why asking)

Could be a few things, I assume you can't trace it back?

If not, switch your mains water off and open you upstairs and downstairs cold taps. Also switch off the central heating pump. Pipe slice the end off and use a compression isolating valve. (make sure its closed)

Switch water back on and close taps, gently open the isolator and if you have lot of pressure it's probably a cold mains.

The slightly warm to the touch when heating is on suggests its a capped flow / return for the central heating. If its capped it wouldn't be able to flow so would heat via convection and not heat up as quickly as a rad.

2. Would the 22mm supply to the bath cold tap be direct or from a header tank?

It's likely to be a cold mains, not from header tank, but if you want to be sure go into the loft turn the big round red handled valve feed from the header to close it. See if you still get cold from the bath still if you do then it a mains cold.

put your palm across the tap outlet and turn the tap on, if you can hold the water back it is tank fed if the water is pushing past and spraying out then you are looking at mains pressure.
if you are fitting an electric shower then you will need mains water unless it is something like a triton T90xr which is designed for a tank fed supply as it has a pump in it to overcome the low pressure or use any electric shower and fit a pump

Have you no other option and can't fit a traditional shower? Ime even the top end ones I've fitted are poor on flow rate when you want them hot. If it's your only option then you'll also need a big feed from the mains electric, usually a dedicated 6mm rated quite highly.