Due to a new TV unit that's soon to go in I need to move my wired room
stat.

For simplicity I've decided to get a wireless one.
My CH is the old school type, not a combi, tank in the loft, h/w cylinder
etc.

So far I've used my mains tester that confirms the CH on output from the
timer goes to the existing stat, which switches to a yellow wire, using the
mains tester & switching on/off, I've traced the yellow wire to the wiring
box next to the pump & motorized valve. Yellow wire is connected to a white
wire that goes to the valve.

From my research all I think I need to do is, remove the old stat, then
blank off the box, which makes the yellow wire dead, stick the wireless
receiver at the other end by the pump, wire in a permanent L & N to it &
stick the white wire going to the valve to the receiver's 'CH on' terminal.

Does this sound about right or have I missed something?

CD