JohnMo

PIR has almost zero noise stopping capability. I would be more tempted to have a dense mineral wool between studs. Then full sheets of 25mm PIR above the joists if you have head room. This would get rid of any cold bridging, alternatively but it at the bottom of joists. You will need to ensure design is ok for condensation risk. UFH design, make sure it's well thought through. Chipboard is an insulator, the pipe are likely to retain the pipe heat in the location of the groove, and not across whole floor. So you need aluminium spreader plates also. You want zero air gaps anywhere as air is a good insulation also. I did fully follow this advise and UFH in a summer house just didn't perform. So much so I put in other heating.

If a leaky house MVHR just means more heat loss, not less. You are adding ventilation on top of everything leaking in. You would be better doing dMEV or MEV run on a humidity need only with matching inlet vents in dry rooms. 1. You don't need software a bit of paper and a one is fine. Find you longest duct route for supply and extract, this is the master route. You need to datasheet for each component within the master and see what the pressure drops are and add them up. Then look at the datasheet for the MVHR and see where you are on the fan curve. Before doing the above you need to understand the room flow rates. You only look at the most onerous route not all of them 2. Ideally insulation should be closed cell or cover with vapor barrier, so you don't get condensation issues.

Yep

4 bed house 125mm inlet out sounds way to small, is the unit big enough. Half arsed because it's cheap, likely to be noisy and not perform well. Have you done all the pressure drop calcs to check you actually get flow rates you need? 1 use insulated ducts - foam ones. Do presume drop calculation - is it ok for the unit? Everything in loft needs insulation. 2 not really, if in unheated loft you need insulated manifolds. 3 I mix and matched, as long as you use the same sizes should generally be ok. 4 between MVHR and outside world and between MVHR and manifolds. You are trying to stop noise from getting to rooms.

My headspace likes the Scottish system, it's a bunch of black and white steps. Do yourself a big favour read Scottish building regs. Once you have the warrant, building control generally visit 3x, at foundation concrete pour, prior to plasterboard and at completion.

Planning permission is pretty similar to the rest of the UK, maybe a few different details, but essentially the same. You then need a Warrant to allow you start building. You need full construction details, a structural engineering certificate, and an EPC based on your drawings. So pretty similar to building regs drawings. But you cannot build until approved.

There also looks to be gaps between aluminium plates and the floor boards. This and the things mentioned by @ProDave can all make for poor performance. Requiring high flow temperature to compensate.

Couple things with the UFH Was there an air gap between the aluminium plates and floorboards? Any gaps acts as insulation so reduced effectiveness. Do you have a drawing of how the UFH was actually done as in the layers from bottom to the finished floor?

For me would look to eliminate the buffer all together and move the heating to a single zone. You have so many pumps, all need power and will eat through electric. If you can eliminate all the zones and run out loop. 1. Heat pump will just supply the UFH directly no pumps or mixers needed. Good chance you can run the whole system cooler, as no mixing will occur. So you get a better CoP. You run cooler, because mixers are gone and without buffer mixing in there doesn't occur either. 2. You eliminate at least 2 pumps. They will pull approx 60W each, run most of the time over the heating season, so 0.060Wx2(pumps)x24 (hrs)x180(days)x£0.25 is £130 cost savings a year for pumps alone. 3. You will have to do some loop tuning to get system balanced. but could save around £200 per year overall Things you need to sort out. External insulation where you enter the ground. Then Seal the conduit end before you get mice living there. The ideal place for your controller isn't where it is, it should be in your hallway or somewhere that represents house temperature. Insulation needed on hot water circulation from cylinder. Look to add 25mm wall thickness insulation to those pipes. I would look to add a timer to the pump also if one not there already. In fact whole cylinder pipes insulation.

Mine was installed 2 days before they changed from 10 years to 15 years

Why limit yourself to octopus or Daikin? Don't octopus use a design temperature of 50 degs for heating? A design temp of closer to 40 would be way better for efficiency.

Do you have a big enough site for the size house you are trying to cram in. Smaller house maybe, or look for a bigger plot? You can almost touch the next property, not sure housing estates are that close. Design smarter, get rid of the dead space inside, design to the plot size, tom fit comfortably. Your first post mentioned resale value and 3 v 4 bed, but house is crammed in to small site, I would just drive past, wouldn't bother looking inside. Wouldn't matter how many beds it had.

So room temperature are fine? If rooms are warm enough is this an issue? Floor surface temperature is just above room temperature, so well below your body temperature so will always feel cool to touch.

A loft space is supposed to be well ventilated. The floor of the loft is insulated to keep heat in the house. Adding insulation at the roof line does nothing except waste money. Best way is to insulate is take floor boarding up insulate ceiling with about 400mm of insulation then use floor board risers and reinstate floor - if you really need to. Use as an opportunity to get rid of stuff that maybe been up there for decades. Keep the eaves ventilation open.

Just a major brand instead of something you've never heard of. Sure Screwfix or similar have a selection.

I used a DeWalt air driven 1st fix nailer, with serrated shank nails. Be careful are they actually 45 x 45, ours came supplied as 45 x 50mm.

Several sorts of turbine. Aero derivative gas turbine, basically go through gas purge cycle to ensure any free gas evacuated from the turbine enclosure and the turbine itself. This can be 1 to 5 minutes, then will go into a start cycle and take full load almost immediately. Industrial turbines, a similar process, but takes longer to take full load Combined cycle turbine (gas turbine and steam turbine combined into a single package) is pretty much the same as above for the gas turbine side, but the steam side of the plant takes quite some time as stated by @Dillsue says. But will output about 50% load until the steam plant comes online - depending on exact package.

Or a slightly less alarming version, the air in the water when first filled has released and the water now occupies slightly less volume, so pressure is slightly lower.

Because he has taken possession of your house, and everything in it for a monthly fee. So why shouldn't he? Bit like saying I spent loads of money on the heating system, so you can't use it to heat the house. I've diverted the pipes to next door where I live. So why should you have control over the electric supplies in the house you rent out? It's nothing to do with you, you may own it, but while you take a rent it's not yours. If I was living there I would just turn the inverter off. Then say you cannot enter.

Except in Scotland - today we are being provided by 100% wind, but at gas prices

Your other issue is the immersion is at the bottom of the cylinder and the probe you are showing isn't at the same elevation. So the immersion and the probe are reading different places in the cylinder, so will see different temperatures. Slip it back together and get on with other stuff. You temperature probe is just a variable resistor, it either reads or it doesn't. It's pretty black and white. As @JamesPa says hold it in place with some insulation, it will read more realistically, as you don't get cool air drawn into the cavity.

ASHP temp sensor is what you have in you hand. It works with ASHP controller to tell ASHP to heat the cylinder. The immersion has its own thermostat under the white cover, it also has a safety thermal cut out, to stop the cylinder boiling if the immersion thermostat fails. If you are heating via immersion the cylinder will heat to whatever the immersion thermostat is set at. It will ignore any the ASHP says. Mine is set to max, so it heats to around 73 degs with enough excess solar.

Have you been specifically asked to provide one?

sorry life is way to short for that nonsense.

Depends. I pay 6p per kWh for gas and two rates for electricity 13p and 29p. Add to the gas cost and efficiency of 85% the actual cost is nearly 7p for heating. If running a heat pump at night I get a CoP of between 3 and 4 depending on outside temperature. So 13/3 is 4.3p and 13/4 is 3.25p. So for a heat pump run on cheap rate, electric is quite a bit cheaper. Running in expensive period a heat pump is about the same cost on a cold day a limited expense. On a standard tariff of 25p for a normal punter I would get an average SCoP of just over 4 to 5 so then it's cheaper at all times of the day, to heat via a heat pump. Add a battery and PV it gets way more complex, but overall cheaper again for electric heating via heat pump. So overall on a new build you are not correct.