I would fit this to the heating side
https://www.rfsolutions.co.uk/remote-control-systems/mainslink-the-5km-original-switched-live-cable-replacement-solution/
And use the cable core eg old switch live for hot water
Internal limescale ? No
Not for a novice as if mains could end up flooding the place
1/2 rubber washer tap cartridge
There’s loads eg different spline count to match the head
Pump pliers will damage them
good evening betty
No if it is an unvented turn mains off and let the hot water run and it will stop prob around 3-5 mins
There might be a smidge of water that comes out when you undo the flexis but a towel below and just quickly swap the flexi for the iso valve as will fit the existing nut...