ProDave

Just to clarify. is the joist running parallel with the light fitting? or crossing it perpendicular? The number of cables suggests it is wired "loop at light" can you confirm? If so I would cut a small hole in the plasterboard straddling a joist. Yes really. This will give you room to terminate all the cables with maintenance free terminals in a suitable box with just one outgoing cable to the light fitting. Screw the square of plasterboard back to the joist, easy as it was cut straddling the joist, fill the gap where it was cut and paint.

Ok dumb question. both those vans are "Psv'd until ....." What does that mean, google does not help me.

Ovens take surprisingly little so I would go with that. Click make this handy double appliance cooker connection unit, swap the existing one for this to connect both the oven and the hob. https://www.tlc-direct.co.uk/Products/AA45DCOP.html

In a house close to passive house levels of insulation and air tightnes, yes, in a 1920's house, almost certainly not.

Probably not. Induction hobs are usually high power. Are there any other rating plates or other info, even a make and model number.

Change the cloakroom extractor for an icon fan https://www.airflow.com/products/icon-range That has a mechanical shutter that closes when not in use. With one source of draught closes that might be enough.

But the OP says he has four 2 port valves, so that would need some plumbing changes. Agreed, an off the shelf solution otherwise. Just another example of a system being "designed" with no proper thought.

That's a different flow switch to mine. If no obvious issue, i would be tempted to buy the same switch head but with a lower flow rate to make it less fussy. Even if the flow rate is a bit on the low side it would trip on a different error if it was really an issue.

Use the one that comes with the fridge.

You don't want the heating to stop whenever the DHW timer is on, only when the timer is on and the tank thermostat is calling for heat. A relay, energised when DHW is calling for heat, to cut off power to the heating would do the job. Or you could be more clever and use the changeover contact of the tank stat to feed DHW or heating. Would need a little more thought depending exactly what timers etc you have.

No. But most motorised valves take less than 10 seconds to open, and there should be some form of automatic bypass valve to give some flow even when all motorised valves are shut. If you suspect this is your issue, you can manually open most motorised valves, so do that to one of your valves and see if the CH14 error stops.

From my investigations, the LG heat pumps expect the required flow to be achieved within 10 seconds of the pump starting. If your valve takes longer than that to open you will have a problem.

Fit battens vertically matching the 600 centre stud spacing, that is all you need to do. to make life easy for your sparky, leace a gap in the battens at 450mm above floor and 1150mm above floor in case he wants to run socket and light cables horizontally.

I too was disappointed with the offerings for built in microwaves. We also settled for a combination oven and bemoan the lack of a turntable (a cheaper brand than yours) and we found in our case things heat better if much nearer the back of the oven. The choice the consumer has is get a combination oven that properly matches the main oven in styling but has the compromises and is a poor microwave, or get a proper microwave that so obviously is a free standing microwave with a front plate stuck on that tries to make it look ever so slightly like the normal oven but fails miserably and still looks like a free standing microwave with an extra bit stuck around it to fill the hole.

With the U values you are having (good) you will struggle to get different rooms at different temperatures. We have no heating upstairs and the upstairs only gets heat from downstsairs, and the coldest it has got in the bedroom when it was -10 outside, was 17 degrees (downstairs 20 degrees) If your top floor is just a gym, which you probably don't want overly hot, then I would not bother with any heating in it at all. This was a bit of a leap of faith. Plenty of people had told me no heating needed upstairs, and coming from "ordinary" houses I simply did not believe this to be so, and like many before me I put electric points in the bedrooms for an electric panel heater so that when it got too cold they could be heated. Those remain unused as they do in many others who did not trust the no heating needed concept and put them there just in case. I expect if you don't heat your gym, you will put some heater points in.......

You can check the flow switch. It will need a partial drain down (easier if your installer fitted isolating valves in the flow and return to the ASHP) Once partially drained you can remove the strainer filter and check for debris, and you can lift the float switch out of it's housing, on mine it is 4 little screws and the switch itself lifts out of the housing but it was not the easiest thing to reach. Then you can check the flapper of the switch moves okay and there is no objects stuck to the flapper. Make sure you put it back facing the same way it came out.

You are not going to solve this by keep on re booting it. The flow is measured by a single flow switch inside the heat pump. It turns on when the flow rate reaches the minimum required. There is only one flow switch so it will be measuring the flow rate at the time which might be heating or it might be hot water. If it does not turn on, the flow rate is too low. If it had previously worked reliably, it might be the strainer filter inside the heat pump is blocked. Have you tried checking that? Otherwise you will have to do as I did and increase the flow rate some how, I fitted a second external pump to do that, but changing the internal pump (small wilo pump in mine) for something more powerful may be another option?

Not meant as a serious post but.... This thing has a screen, so you can see (via the ring camera) who is at the door, and it has a speaker, to go ding dong when you press the button. Replace with an old school wired door bell with the chime unit in a more central place in the house, and a spy hole through the door to see who is there. No need for the shelf and you will wonder why there is a socket there. I'll get my coat.

Can you post some pictures of this 15cm deep monstrosity? from front AND back?

I am convinced the only way the average building monkey will ever get a room in roof right, is to make the entire roof a warm roof. Fairly easy to detail, then all the roof space even the bit not used for the rooms, is inside the warm envelope of the house.

Yes. As much as you dare without bursting through the back of the breeze block. 25mm back box, flat plate socket, should be able to end up with the face of the socket well back from the plasterboard so the wall wart won't stick out much, if at all. Might need to recess the plaster a bit below the socket as well as the wall wart hangs below the socket. I have done this several times for ultra flat tv brackets so the socket and plug does not stick out from the wall. Or can you just not find a much slimmer device, I mean 15 CM deep is ridiculous these days.

What is the build up of the wall? Recess the socket in the wall (I do this behind wall hung tv's) to the wall wart does not extend in front of the wall. Does not matter what it looks like, it is hidden.

Zoom in on picture in OP and it is centre positive.

I would want to be SURE that really is the case before spending money. I find that hard to believe as you should have 13kW available at air 0 water 35. Unless they have been "faulty" right from new.

Probably but anything different would no doubt invalidate any guarantee. Can we see a picture of the whole thing in situ so fully understand the "problem"?