Your original valves if the same as the first picture would of just required a nip of the glad nut quiet normal for them to weep if not used / operated for a while
As for leaking all I can suggest is to drain down to limit damage and...
You can get rid of one of those extensions 100% possibly both by lifting the trap up if the washing machine spigot piece is too long cut it down as you have a removable nut on that one correct ?
Also what’s the kitchen sink plug top /...
Downstairs would recommend as plaster is easier to patch than laminate/ different flooring
Depends are you 100% sure it’s not leaking from above and running down
As for cost 2 hours seem optimistic especially draining down and...
On the danfoss programmer leave hot water always on eg permanently
As for room stat there maybe a sensor inside size of a tick tack box with danfoss on it with no controls / adjustments just a box with a grill on it this tells the...
Slowly increase the pressure you will see it climb in 0.2 or 0.3 mbars leave it till at correct pressure then slowly shut off if you go over remove the hose from the fga not the meter stnd run 1 mbar 1 second out / off
Put the tube on...
Change wc elbow for a tee and put shower and basin into that via a 2” pipe note this will have to be vented via an air admittance valve eg aav
Install a tee into the 110mm orange drain pipe for the bath and washing machine via a 2”...
Need to span the gap with 20/25mm metal conduit so not to compress the foam
As for fixings is it hollow block eg two cavity’s on each block or solid blocks ?
Is the gravity cold fed shower connected to a combi or unvented cylinder for the hot?
If so it's most likely higher pressure hot crossing over into the low pressure cold via the shower mixer or possibly a mixer tap elsewhere with L.P...
On my version of your photo, if the bath waste is as identified then the best way if you can access that pipework is to remove the access cap circled yellow, use a snake / flexi and push it down towards the stack first, there's only one...