ProDave

As above , if it is just a workshop / shed (i.e. you don't intend to fit a car in it) I would be very tempted to have two buildings within the size limits for permitted development and not requiring building regs. Given the aparent L shaped nature of the garden from your plan, I would personally tuck the building(s) just around the corner to the right so not obstructing the straight run of garden from the house.

Yes is does sound like it is not shutting off. Only way to find out for sure is remove it, then you might as well fit the new one. PITA having to drain down to do so.

^^^^ Ah yes safe zones. Everybody know never to drill a hole in a safe zone without checking first. Except the person hanging something on the wall, and then of course they measure meticulously to ensure the thing they are hanging exactly lines up with the centreline of the switch. BULLSEYE

These actuators are a pain to test as they don't work with the actuator off the valve, the mechanism relies on being on the spindle of the valve and just won't work properly if you try and energise it off the valve. I always find it is difficult to tell if water is flowing as you don't have a flow meter, you can only go by is the water hot both sides of the pipe etc, so when it closes you have a while to wait to see if the pipes cool down or not to confirm if it has closed and water has stopped passing.

You should be able to shut it off with little force. Does it turn freely with the head off? It will only turn roughly 90 degrees, and as you say the closed position should be a soft stop where the flow is plugged. If the plumber could not check that and passed the buck to an electrician, time to get another plumber. Is the valve seemingly opening and closing correctly with the head on? Can you see it rotating?

Better than that, but no photos. Drilling a 16mm hole through a thick stone wall for a cable. When it broke through on the inside, I cut back a bit of the plasterboard, to find the drill bit had emerged through the wall between two 22mm copper pipes that nobody knew were there. An inch either way and it would have been a wet problem to fix.

A previous job, one of the engineers never seemed that bright to many of us, and nobody was really sure what he was doing. Then after a while he was sacked and marched off the premises immediately. It turned out he was spending most of his time running his own business.

Thank you for coming back and reporting the outcome.

How much do the water company know or want to see? If nothing, just make sure the pipe they are presented with is 25mm and the correct depth. They don't need to know it then goes to 32mm. Don't even mention that unless asked.

Yep that's a back to wall pan with a flush pipe. NOT a close coupled pan with a donut and a clamp to pull the cistern down onto the pan. If you choose to change the cistern, probably best to use the existing flush pipe that is already cut to length. You assemble the fill valve and flush valve into the cistern and fill the cistern with water before you fit it, so you can leave it a while and check it is not leaking from either the fill or flush valve, if all is well empty it and continue fitting. If it then leaks it must either be from the flush pipe at either end, OR the waste pipe coming out of the pan if the pan connector is leaking.

Check your cold feed pipe location. Most concealed cisterns have bottom entry but looking again at your picture yours appears to be side entry. @Nickfromwales are you thinking of the donut on a close coupled cistern? I think this is a back to wall pan against a ready built unit with concealed cistern and a flush pipe.

This one looks like it will fit, but check carefully that the dimensions are no larger than the actual one you have before buying one. https://www.screwfix.com/p/etal-porto-dual-flush-concealed-cistern-4-6ltr/110vn#product_additional_details_container I was mainly looking at size, but if it does fit, then at that price I would buy 2, and keep the spare in the loft for next time. EDIT it is more important to measure the unit it has to go in. there are others on SF that are wider than the one you have, but that does not necessarily mean they won't fit. Post a picture of the empty unit and measurements please.

WHERE is the leak? Why can't the existing cistern be repaired. that is likely to be easier.

I like that layout, you can see the fire, you can see the tv, you can see out to the garden. Perhaps a motorised tv mount to swing it out a bit when in use? And the unit below solves the age old problem of where to put all the "set top" boxes. Always a problem with a wall hung tv.

That is a very personal choice. A lot depends on your sofa. If you are watching a tv at roughly seated eye level then it does not matter. But what I found visiting a relative with a tv above the fireplace is it got VERY tiring with your head constantly tilted looking upwards and a low backed sofa. It would imho need a sofa with a high back so you could rest your head against the high backrest to begin to make it bearable for me.