ProDave

And don't mention it on an internet forum......

Re the landing cupboard. Do you really want a dressing room with the odd angle at the end? Why not square off the end of the dressing room, and re create the cupboard from the landing that would get wider the further in you get?

Just look up the spec of the old boiler and get a similar size to that. There are some misconceptions about UFH. You say it did not get as warm as you thought it should. But did it heat the house? Because UFH heats over such a large area if does not need to get "hot" like a radiator. It just gets warm. That is how it is supposed to work. Depending on how much insulation in the house it might only need to get a few degrees hotter than the room temperature, so barely perceivable as "warm" which a lot of people mistake for "not working"

Very personal opinion but I completely dislike the "island" bed arrangement. Is that a full or part height wall behind the bed head? Personally I would have the bed pushed back against the main entrance wall and I think you will find the room feels so much more spacious with a decent space at the foot of the bed.

In the 2 1/2 years I have had my solar PV, i have exported 283kWh. The rest I have self used. Assuming 5.5p export payment, I would have received £15.56 so far. I will let you do the maths and work out the payback time on the "MCS premium" Just get a competent electrician to install it for a lot less money, then ask your BC inspector to show you where in the building regs it states they must be installed by an MCS company.

WHY do you want MCS certification? The only tangible need for that in the past has been a requirement to claim the FIT. But with no FIT any more, why would you want to pay the "MCS Premium" for a bit of paper that is worth virtually nothing to you?

Are there gaps between your cladding planks? What are you doing about insect mesh?

My home made solar PV diverter works on burst firing in a half second window and it logs the time the immersion heater is on from which you calculate cumulative power going into the immersion heater. For those interested, burst firing works, because electricity meters work on an "electricity bucket" principle. Once a watt hour has passed through the meter it is registered. But if a fraction of a watt hour is imported, then the same fraction of a watt hour is then exported, that can be repeated forever with nothing being registered. I worked out with my immersion heater on, it would be consuming a watt hour in just under 1 second. So I chose my burst firing time as 0.5 second. So in each half second my immersion heater can be on from 0% to 100% of the time, according to how much surplus there is at the time.

The net result is the same. Any that claims to be varying the voltage will be using phase angle firing just like a light dimmer so it is only on for part of a cycle.

The 11KV is just that, hight voltage 11,000 volts. This is the feed TO the substation, which is the pink rectangle in the bottom right. Your supply comes FROM that substation. For minimum cost to you, you just need to find what you can connect to just by jointing into the cable going past the front of your house. Clearly you cannot get 3 phase that way. What is not clear is for the 3 phase option, do they have to just dig 2 holes and make some joints, or is that a new section of cable to be installed between points C and F? If tat is a new bit of cable tat goes some way to explain the cost. I am near certain a single phase connection, if it is within te existing capacity on the cable going past your front, will be substantially cheaper.

WHY did you ask for 3 phase? The first thing that stands out is "Breach joint into 4 core cable as customer wants 3 phase" So choose single phase and that looks like one hole in the road and one junction not needing to be made. 35mm 1 CAL is 1 core concentric aluminium cable. Think of an overgrown super sized coax cable. That is the standard supply cable used mostly. What did the single phase quote say, how much cheaper was that? Post the entire wordy bit of the quote, that will itemise where all the costs are. (anonymise it of course) If you have not asked for the single phase quote, ask for 21KVA. Then show us the exact quote. IF you find they are asking for network upgrade costs, then try a lower rating, our supply is only 12KVA and that is plenty for a low energy house. How are you going to heat the house?

That comes back to where is the thermostat pocket. With ours 1/3 of the way up the tank, the ASHP will come on not long after a decent length shower as been used. If we risked it not coming on, that is when you get into dangerously low for the next shower. My philosophy is slightly different that I try to not use the ASHP at night, preferring it to run in the daytime when there is PV generation to help it along. I don't have dual rate electricity though I always keep that option open.

I would say a PV diverter is essential in making solar PV viable now without any feed in tariifs. Roughly 1/3 of what we generate ends up in the immersion heater and that is despite best efforts to self use by using the big appliances in the daytime etc.

What size of ASHP are you planning? This is one issue with them, they don't heat water as hot, and they take longer to do so than a gas or oil boiler, depending of course on the size of your ASHP. Ours is only a 5Kw ASHP with a 300 litre tank so it does take a while to re heat if all used up. We heat the HW to 48 degrees with the heat pump so it will use more hot from the tank than it would if say heated to 60 degrees with a boiler. I have "solved" this issue by fitting a modulating instant electric water heater on the output of the HW tank. It is detailed in this thread Most of the time the electric heater does nothing, but if the hot water starts to run cold, it powers up and tries to maintain 48 degrees output. At the very worst case, if the tank has gone completely cold and is only supplying cold water, it will still maintain some warmth or if you turn the shower flow rate down, it will maintain full temperature at a low flow rate, like showering with a 10Kw electric shower. Another point worth making is the positioning of the temperature probe in the tank is important. Most ASHP's are provided with a temperature probe to put in the tank. I did not give this enough thought and even the lowest pocket is about 1/3 of the way up the tank, so the tank could be down to just 200 litres of hot water before te ASHP even knows it needs to turn on and start heating it. If I were specifying the hot water tank now I would have a thermometer pocket lower down, probably several of them near the bottom of the tank so you can experiment which one works best.

Also, as a matter of personal opinion, I would buy the old NTE5A, much more robust and versatile. I hate the current NTE5C so much harder to terminate and that silly clip on front plate is hard to unclip if the socket is close to a corner and easy to break trying. You can also get a filtered plug in for the NTE5A to separate landline and broadband, so extension telephone wiring should not affect your broadband performance.