ProDave

Well done. At least you have a buyer and are exchanged. Everything you need is now in place.

A tip I learned for kitchen door handles, is make a jig. A simple bit of plywood with 2 bits of wood fixed to form an edge so it sits onto the corner of a door, and your handle holes drilled in that. No need to mark out individual doors, just place the jig in position and drill.

I was offered 12KVA at just connection cost, anything more would mean paying for some upgrade. So I took it. The reality is I have the same 100A supply fuse as everyone else and connected to the same 100KVA transformer. Your 80A connection will be fine. Perhaps not do lots of welding while dinner is in the oven.

Regardless of any assurance, before ordering windows I would MEASURE the actual window openings as built. I paid a local builder company to build and erect my frame, and then later paid them to supply and fit windows. Even they did not trust they had built the openings to the drawing, and measured them before ordering windows.

What channel did you use? Unistrut? Where did you get long lengths locally?

Re hard to reach smoke alarms. All ours our Aico, hard wired mains powered. I also have the Aico remote control unit that allows you to test the alarms, silence them in the event of sounding, and locate which one has caused them all to sound. That is a wireless connected unit that you can mount anywhere, or use it portable, so no need to get the steps out or do the tea towel dance.

Let us know how you get on. Our supply address started as a silly "land 50 metres west of..." address for the supply that was put in very early. With out previous supplier, I changed that to the actual house address. Previous supplier went bust and we got swapped to Octopus. The address reverted to the original one. So it is not just the address your supplier uses that needs updates, it must be on some DNO database as well. I have not bothered the silly address does not bother me. It might be of more concern if you wanted to switch supplier.

for the DC runs, easiest to buy proper solar PV DC cable, sold as singles usually 4mm or 6mm and run them in conduit. Probably best to have a DC isolator switch next to the panels, and another where the DC cables go into the inverter.

Does it run from it's own boiler? or does it share the output of the house boiler? UFH does take a long time to heat up. It is best run to be on most of the day, some run it all the time. To set the flow rates can be a long process, run it for a long time with all the room thermostats turned up high, the rooms that get too hot, turn their flow rate down, the rooms that are cold, turn their flow rates up. You are aiming to get all rooms to heat up at the same time. The red knob at the bottom is an automatic bypass valve, you don't need to do anything with that. The black knob below the pump is the mixing valve and sets the water temperature in the UFH loops The little guage top left of the manifold is showing the water temperature, looks to be about 40 degrees, I would not go any higher.

Start by assuming it is working properly, and describe the problem you are having with it? Is is just that you have never had UFH before, and you expect it to work like radiators, to come on, to quickly feel warm, and to quickly heat the room? Of more interest is what user controls do you have, a time clock or programmer of some sort? A wall mounted thermostat of some sort?

What will most likely happen is the "24 hour supply TC" section will not get connected at the smart meter swap, so that section, your panel heaters and ASHP will not work. Simple to correct. Your meters are separate, outside in a meter box I presume, can we have a picture of that.

Usually when swapping off the THCT system to "normal" E7 the total control CU gets left disconnected, so only the normal house circuits and off peak circuits work. This is because there are only 2 metered outputs on E7 and they have 3 connections, and the meter monkeys won't join 2 together, that is a job for an electrician. How to sort that out depends a lot on what consumer units you have. It was common at the time to use a custom Wylex fuse box split into 3 internally with 3 separate main switches for the 3 different systems. So solutions range from re configuring that back to a 2 system box, or just joining 2 of the feeds together outside the CU with a Henley block. Post a picture of your consumer unit(s) and we can advise. Off peak does not make the sense it used to, the rates on offer just don't seem to make it attractive.

The issue seems mostly getting storage heaters to turn on and off in time with the cheap rate periods. And of course in the case of THTC just fitting a smart meter, timed or not, would usually leave the always on cheap rate supply disconnected.

The whole radio teleswitch replacement is a fiasco. And this is directly related to that. THTC in essence is just an normal E10 install with a switched off peak supply, but then with the addition of a second meter that is permanently on metering a heating supply. It was a creation to try and improve on the main drawbacks of the simple off peak tariffs. Used properly, in @Crofter case the A2A heating could have been connected to the heating circuit and got the cheap rate 24/7. None of the off peak supplies or THTC had remote meter reading, so could have been kept working by replacing the radio teleswitch with any other form of timer. Prior to the radio teleswitch system a spring reserve machanical Sangmo Weston time switch used to be used. I hear so many horror stories of trying to get E7 working on a smart meter that it would put me off trying and just go for a single rate tariff, even of you have to choose one of the off peak rates first to achieve that.

Examples of the adjoining other garages on the site might be useful at least from a planning perspective.