ProDave

So what refrigerant is this using to get to 75 degrees? And can it still do that when it's very cold? e.g -15 here this morning (new record for us) so it would be trying to heat DHW to 90 degrees above air temperature.

At the moment they are NOT getting hot, they are getting luke warm and not able to put enough heat into the house. I am trying to establish if the reason for them being luke warm is because the ASHP is set up wrong, or if there are more radiators than it can cope with. Do it by measurement, for ages you have been telling us they are "hot" which is why people have been questioning the insulation etc, but when you got the thermometers and told us they were barely 35 degrees, that is NOT "hot" so because of that wrong information we may have been barking up the wrong tree.

Is that the plumbers blood?

No. I thought my suggestion was clear. I think part of the problem is we are making what we think are clear suggestions and you are simply not understanding them. I am trying to estblish if the reason the radiators are cool is because the heat pump is not set up properly, or because it is under powered and simply cannot cope. Knowing that might offer a way forward. So what I am suggesting is you go round and turn off the lockshield valves on all of the radiators except one. I suggest you leave the one in your cold bedroom as the only one left on. then leave the heating system on exactly as it was and let us know the flow and return temperatures on that one radiator that is still left on. Two outcomes. That radiator gets piping hot and your cold bedroom becomes warm. That would suggest the ASHP is set up correctly but is simply under sized and cannot cope with all the radiators. Other outcome is that one radiator that is left on is still only luke warm, which suggests the problem is settings within the ASHP as it damned well should be able to get one radiator piping hot.

Please do that only 1 radiator on test and we can start to make progress.

Your "other" sounds about right. We average about 100kWh per week on non heating / non hot water usage, a figure I just cannot get down (how anyone gets to just 2kW per day non heating usage beats me, they clearly don't watch tv, do any washing dishwashing or tumble drying)

I would read that as being a 3/4" one end to 20mm the other end adaptor. I would leave that alone. Cut into the pipe on the right hand side where you can be more certain it is 20mm and fit a tee there.

You make the room, put 2 smaller rads in, or accept it is going to be cold.

I will be very interested to hear how this works. Apart from the cladding, it looks to me like the heat pump unit is mounted too close to the wall to start with.

I suspect that is just irregularities in the render showing and it is just decolouration. I am finding mine at 4 years old is starting to show discolouration from weathering which is moss / algae growing and I am experimenting with spraying it with a mist of water / bleach mix to kill it.

190L at 55 degrees won't do a 5 person house. Who claimed that? Vailant themselves or some third party? You won't get much more than 55 degrees from an ASHP you either need over sized radiators to work with that or under floor heating. If it is an old house, make sure you really know how much heat you need, most disappointment seems to be when you need a lot more than you think and the chosen ASHP can't deliver it.

I have one of these https://www.machinemart.co.uk/p/cst6-heavy-duty-3-in-1-sack-truck/ Bought it 20 years ago when building the extension to a previous house. Had much uses since and still going strong. Not the best construction, but adequate and it has not broken yet.

UFH and system flow / return are all one circuit and get filled together.

Hand pump is just for pressure testing pipes part way through install. To re fill yours you just open the two valves at either end of your fill loop and watch the pressure gauge that should be somewhere nearby, probably under the expansion vessel. Turn off the fill loop when it gets to desired pressure. Go and bleed the radiator. You will have to repeaat a couple of times, re pressurise and bleed again until no more air left.

Then do as several of us have done, leave your meter box on the boundary and run TWO submains from there, one to the house and one to the garage when it is built.

^^^ But 6 by 6 metres is over 30 square metres so will need building control.

You solve all these problems by having the supply routed into the garage, have as much switchgear as you want in there, to feed whatever you want, and then one submain from there to feed the house. As for electricians turning your house into a collander, design it properly with a service void on the inside of the sealed envelope and you keep a nice air tight house.

I might have to buy one and play with it.

Yes the Sunny Boy inverters, knock it with your knuckle nice and hard.

Last nights build in the Fens didn't have any particular points of note, other than i could not believe the crane driver when the crane sank in the soft ground trying futile attempts to shift it to the point of smoke and various fluids pouring out. Poor crane.

Planning is needed for it because of it's location, not size. Building regs is needed on > 30 square metres, might even be a smaller amount.

That's fine, the inverter limits it to 3.68 so that is G98 and can be installed without needing permission and notified after install.

A monoblock ASHP is just flow and return just like a system boiler, and some motorised valves and a pump or 2. Read the Flippin Manual. I don't know why so many people treat it as witch craft.

Yes usually the inverter menu's only work when the sun is up. What size is your PV? Has it not been registered with the DNO yet? It is the inverter that limits the OUTPUT to 3.68kW so that if nothing is being used in the house then no more than 3.68kW can be exported. If you have more than 3.68kW then it's a G99 install and you need permission from the DNO BEFORE it is connected. Don't always assume permission will be given and there may be a cost.

ASHP will cost more than a boiler, but probably similar to cost of gas boiler AND gas supply connection. ASHP can be DIY installed if you are competent, gas can't Actual install of ASHP or gas boiler ought to be very similar, the problem is a lot of plumbers and electricians won't touch them because they think they are difficult and ar not prepared to read an instruction manual and learn. The rest of the heating system, UFH, hot water tank etc is the same regardless of heat source.