ProDave

We used ibeams for the ground floor, no services under there other than services coming up through the floor so no cutting of webs. Posi joists for first floor, plenty of room for all services without having to butcher anything. I only wired one house with first floor ibeams, plenty of work drilling the webs and keeping within approved drilling zones. the plumber seemed more "flexible" about where and what size he drilled. Why make it difficult?

Yes all outside walls and service battens in place before first fix. I have tried once, to first fix before outer walls complete, you just have to leave lots of ends dangling to be completed later when the walls are ready, right PITA, never again. The one thing the electrician can do before then is get all the cables exiting the walls e.g for outside sockets, outside lights, ASHP etc, get all those through the wall so they can be sealed up as the final insulation layer goes on and you should then be able to carry on without making any more holes in the walls.

In my case I have the ASHP probe in the centre thermostat pocket and the mechanical thermostat in the upper pocket. The mechanical thermostat is only there in my case to satisfy the G3 regs of an unvented cylinder, to close the motorised valve feeding the UVC in the event of it over heating. But since it is impossible for an ASHP to heat the water hot enough to worry an UVC it is a theoretical possiblility and I never expect it to operate. But rules are rules, it has to be there. @Cyberfruits that link in your post above asks me to sign into google drive or something like that, I suspect that is not what you wanted to post.

The problem with this "whole roof" PV idea is you need to choose the panels at design time and know the size of them, and then design the roof to be an integer number of panels in each direction. And solar panels don't seem to be made to standard sizes. So you either want to order your panels as soon as you draw your plans based on that size, or hope and prey that the size you want is still available when you actually come to build it. Then because supply of that size of panels is not guaranteed into the future, you might want to buy some spares and store them away safely. The next obstacle is a bug bear of mine, we have a stupid system where anything over 3.6kW may not be allowed by your DNO or may only be allowed if you pay for upgrades. If we are going to have lots of PV on every roof, that limitation is the one big obstacle that needs removing.

That is certainly a water thermostat. It is a bulb on the end of a capilliary tube that slides into a thermostat pocket in the cylinder. the grey plastic cover contains the actual thermostat and the fact it is slightly wonky is of no consequence. That looks quite low down for the normal thermostat position, I assume there is an alternative thermostat pocket nearer the mid height of the ctlinder? If you are heating it with an ASHP there is very often a temperature sensor supplied with the ASHP as well.

In my house heat pump power consumption is only about 1/3 of total power used.

Ask the council. If they don't know then it won't matter what you submit.

Can you see where the green/yellow wire that exits the meter box bottom left goes to?

You shouldn't be buying a new house then thinking of ways to bodge a fix to the builders error. I would tell them of your concerns and tell them you will buy it of they re do it properly but are not buying it like that.

Moving the CU to the other side of the wall and poking the cables through may well result in the cable drops no longer being in a safe zone. Easily rectified by say putting a socket on the wall in line with the line of the cable drops.

I would be asking how do you make a roof light a means of escape window? Perhaps English building regs don't require that?

I recessed a standard Hager metal CU. The Hager one had round conduit knock outs that with it recessed come out behind the plasterboard. The only real difference between a standard CU and one sold as recessed, is when you recess a standard one, you have to be accurate cutting the plasterboard around it as the front only overlaps a little. The ones sold as recessed tend to have a larger "flange" around the front to hide imperfections.

The point everyone is missing is this is DHW demand. Yes I can understand the modulation and PID limitations when heating, but the point I would be banging on abut is you have turned on a tap, it should be heating DHW with a completely different set of parameters and control algorithm. The fact it refuses to do that because it previously locked out doing something different thing is a FAULT with the programming. When it switches to DHW it should completely ignore what it may or may not have been doing previously and get on with the job of heating the hot water. Anything else is a design fault.

This is NOT a HMO. That requires planning permission and licencing to let rooms to multiple people. Letting a room or 2 in your own house to a lodger does not and you are still using it as your main residence.

But surely the basic issue is when you open a hot tap the boiler should forget heating mode, and switch, without issue, to hot water mode and heat the hot water to the required temperature. I would be saying you have had plenty of chance to fix this, and you have failed, so i want the boiler removed and a full refund given and I will replace with a different boiler.

That sounds like a lot of waffle that translates into: "There is a bug in the software that under certain heating situations, the controller is unable to switch over to hot water heating and just heat the hot water. And we don't know how to fix it" Anyone disagree?

Were they the frosty days? That is why we chose not to move to the west coast. Cold but dry is not so bad after all.

I often speculate how my house would perform if I just picked it up from here in the Highlands and put it down in say Cornwall close to the coast where frost is rare. It would certainly be cheaper to run. PHPP sets out a max heating requirement per square metre. Does that account for location, i.e. to meet that a house up here would need more insulation than one in Cornwall?

What is wrong with a wet room because you have young children? Make the whole room a wet room, and do as we have, the 2 screens around the shower in that corner hinge away flat against the walls when the shower is not in use leaving a huge open space.

So you already have RCD's in the CU. So I would be looking to verify the cable routing from the meter box to the CU to confirm it does not actually need RCD protection and swap that for a plain MCB in the meter box not an rcbo.

Get an electrician. It might not even need RCD protection on that cable depending on it's routing. Post a picture of the consumer unit in the house as well.

That's an RCBO I bet it is earth leakage tripping it, damp somewhere. How does that connect to the house? what sort of cable and over what distance? Do you have any test equipment like an insulation tester?

Post a photo of this "main trip" so we know what it is.

Always good to get that completion certificate.

That is just over thinking what will the PV power? On that dull day, it will power whatever happens to be on in the house at the time, and if there is any surplus after that it will divert excess to the immersion heater. It needs no user input to achieve that. So the key thing with solar PV (without battery storage) is move as many of your electrical loads as possible to the daytime. For instance I have my ASHP timed to only start DHW heating at 11AM. By then the sun should be up and PV generating. So at least some of what the ASHP is using is coming from the PV. And all big appliances get used near the middle of the day. And there is nothing wrong with the ASHP heating the DHW AND surplus going to the immersion heater as well at the same time. PV conflicts with a TOU tariff such as E7. The TOU tariff suggests you want to do as much as you can at night, PV says do as much as you can in the day. I don't personally like TOU tariffs, they come with a much higher day rate.