ProDave

The first thing I say is do you really really want the HW cylinder in the plant room? Only put it there is the plant room is central to all points of hot water use to minimise HW delivery time. If not, the HW cylinder is often better placed in an airing cupboard elsewhere in the house that is central to all points of HW use.

The main feed will be to the wiring centre. so FCU there. From there you will need a minimum of permanent L and N and switched L (call for heat) to the boiler. So use a 3 core and earth for that, and locally a 3 pole fan isolator switch would do the job of local boiler isolation.

A stone mason would make and install such an arch. It is not an off the shelf product, and it is not a trivial amount of work to fit it either.

Ah this is a "clever" pump, controlled by an APP. Sorry I will bow out here, it is far too complicated and wants to make up it's own mind when and how to run. Not what I would want in my system.

Are you employing an architect or other designer to specify the details of the building and get the building regs approval or are you doing it all yourself? By far the best approach is insulate the hell out of the building and make it air tight. If you are needing to add things like solar PV just to get a SAP pass, then the building itself is not really good enough.

Can you post a picture and more details of this "wiring centre" Without knowing what is controlling the pump, nobody can say id it operating how the system was designed or not. If designed properly, of course the pump will not run when there is no demand.

Do you mean the tank is making a noise when heating DHW, perhaps a rattling sort of sound coming from inside the tank? I had this with my Telford tank. By trial and error I cured it by opening up the bypass valve so it was bypassing water all the time. I think the issue was the heat pump demands such a high water flow rate, that flow rate was more than the tank input coil was happy with. I couldn't just turn down the pump or the HP would trip on low water flow rate, so allowing some water to bypass the tank seemed to "fix" it.

Is the underside of the B&B structure higher than outside ground level?

Then you end up with stud spacing that does not match plasterboard sheet sizes, setting yourself an other problem to solve.

Any competent electrician can fit a diverter so just get that done when the tank is installed.

https://www.screwfix.com/p/crabtree-capital-50a-1-way-pull-cord-switch-white-with-neon/90597

What is needed, is someone who has had a BUS / MCS heat pump install to come and tell us exactly what it cost, exactly how many man hours of workman time took place at their house, and exactly what heat pump and other equipment was installed. Then we could pick it apart into a material cost, and a reasonable labour cost, and see what the "MCS premium" really was. Without that all I can say is "me and my plumber mate could fit it a lot cheaper"

Just after you made a tight turn? I was going to suggest if in doubt, don't make a tight turn just by skidding round, pick up one end of the machine and turn on the tips of the tracks.

Can you imagine the uproar, if Gas Safe was run as a scheme that added at least £5K onto the cost of installing a gas boiler, compared to just paying the plumber? Why is there not the uproar at the added MCS costs?

No, but someone, some group of people, sets the policies that "encourage" customers to use an MCS company in order to claim a £5K grant, and if those people cannot see that using an MCS company adds more than £5K to the bill compared to just using a plumber and an electrician to install it, then frankly we might as well give up trying. Then add into that mix, you only get PD rights for a heat pump if you adhere to MCS rules. Why do I feel this is the next brewing scandal?

Corrected that for you (imho of course)

Crabtree do a surface mount one which is an electricians dream, you fit the switch, connect the cables, then put the cover on without flexing any of the cables in the process. Because you can be sure it is connected well it is very likely to be more reliable, but Customers don't like them because they want flush. Personally I would never have a pull switch shower switch in my house, wall switch every time.

Just one little snipped from that: That about sums it up, admitting the existing system is broken, unworkable and expensive, and needs fixing. While projects like this are good, it is no good just finding a way round the problem for a few streets who have received a grant to do so, the whole system needs to be fixed, so getting a heat pump fitted is as easy, and almost as cheap as getting a gas boiler fitted. Until someone "at the top" grasps the problem, a proper solution for everyone will not happen.

But where he is, timber frame is the normal, brick and block is the niche and has been for some time.

No different to any other cable, if it's only 2 core, you ignore the earth pin. Making it less bulky is a good reason to change it.

+2 Are we a nation that has forgotten how to fit a 13A plug? When I was younger and had a small house, I had a bit of OCD and every single plug in the house was exactly the same type.

I don't think I can help with specifics. The building company I used have disbanded, but in any case were probably too far away to be interested in your job. Some of them have retired, and some are now working in an individual capacity or joined other firms. Just to be clear though a locally built "stick build" like this is exactly the same as if the same design had been stamped out in a bigger factory and all arrived on one articulated lorry. It is not in any way an inferior build. At least 2 local self builders have stick built on site, one all on his own, and the other by employing a general builder to help him.

Our timber framed house was built by a local building firm. They built the kit panels in a workshop nearby, and brought them to site a few at a time on a 3 ton trailer behind one of their vans. That would have fitted down your narrow lane. That is the sort of builder you need to be looking at.

Worth having a look to see what make switch and replacing with the same. A different make may have the terminals in a different order or different position and then begins the hassle of re dressing the thick cables in a confined space so match the new switch. Make sure the terminals a TIGHT then give the cables a wiggle and tighten them again. Any burned cables (usually die to not being tight) will need cutting back to good clean copper.

I could see that if the subsiding building collapsed on your contents and you tried claiming for that but otherwise why? They are insuring the contents not the building. Did they specifically ask "does the building have subsidence" or was it a little detail you told them without being prompted thinking you were being helpful?