JohnMo

I would temp back and really ask yourself why you need 2x heat pumps. Blown air in bathrooms will not be the most comfortable way to heat, especially if you are wet. Have you done a full heat loss survey?

Think the trouble with a lot of these questions and issues, they are raised after the event, when it's basically too late. People expect wonders to occurs without pre planning and deep discussion on expected outcomes. Thermal bridging isn't great, but we have a work force of poorly trained labourers, not skilled crafts people. Only things open to you without taking everything out and starting again, fill all gaps with expanding foam, seal the outside with mastic to form a waterproof seal. But looking at the thermal images, I would comment Door cill area doesn't look that bad, worst bridge appears to be at the side lights, most likely caused by air movement. Your doors most likely need adjustments as you appear to have drafts at the door seals. So as mentioned fill any remaining gaps with expanding foam, seal with mastic and move on with your life.

I wouldn't bet against you. Low gas prices really mean more profits for big corporate entities, not much passed on to the man on the street.

The HE mini store, is a part of the central heating system, in it can be included in the already in place expansion vessel (recheck sized based on increased system capacity) and relief valve etc. Assume ministore has an immersion, it could be heated by that, but will not take much energy depending on the volume. To get the most out of it, you need to set your boiler up to do priority domestic hot water. Which isn't as straightforward with a combi, but can be done. Then you can blast the ministore with high temp (80 Deg) water to ensure you actually have endless DHW in winter and top as needed in summer. Your immersion will hold the temperature while idle, but on hot water draw, will not keep up especially if running on excess PV via a diverter. So get your tin hat ready "the blo@dy hot water cold again" moments with the other half.

That's mixers, they mix, they mix all the time like it or not, always a fixed amount of mixing. They are really designed to operate with high flow temps from boilers, generally not suited to ASHP systems. If you need to mix because of different flow temp needs for two different manifolds it's better to use an electronic mixer driven by the heat pump controller. I had the same issues, deleted the mixers and additional pumps, the actuators on the manifold and just left room sensors in place for monitoring.

So you really need something that does remote access as an add-on, instead of out the box. Then everything is local, with the ability to look at stuff and adjust settings. I have a polypipe system with room sensor main hub and and external WiFi access point. Everything is local, WiFi link of it works or doesn't has no effect on the work of the system. Heatmiser and Wiser I believe are the same. You need an add-on for remote access. Anything that mentions clouds walk away

If you have the space put a proper UVC in. The mini store is unlikely to perform much better than your combi except immediate draw of would be quicker.

£1400 isn't modest in my book. Plus if used the way you are suggesting you would need a full safety group. You may have a few things to resolve. If water flows through the combi it will fire up, so use gas anyway. If heat store isn't heated, sun not playing ball, it would just cool the water already heated by gas boiler. So no hot water! I would install cylinder upstream of the combi, heat by solar, if water is above 45 divert around boiler direct to tap, if below 45 let it be heated by boiler. Saves boiling firing when not needed etc.

Really depends how it's setup. Would think every parameter you mentioned can be adjusted. But neither way mentioned sounds an efficient way to run a heat pump.

Or a dry trap? One or the other sounds contradiction, or your client has money to waste🤔

Where is your structural design? Should be zero need for such questions, if your building is designed.

So is your heat pump oversized to allow this?

Definitely found that with mine, certainly once you get cycle times below about 10 mins, you may as well give up.

So that is just the restart hysterisis. Doesn't the lower pump speed, just drive a lower output of the radiators, and then drive shorter boiler cycles, as there is less to take the boiler heat away?

If settings don't give the behaviour you expect set them back to default. What thermostat are you using? Is it an on off one or opentherm?

Read an article the other day saying electric prices in the UK are set to drop like a stone. As our price is directly linked to gas wholesale prices, which due to the glut of LNG on the world market is falling, and due to fall even further. Several countries are reducing their uptake of LNG due to more renewables coming stream and less reliance on imported gas.

How do you do your schedule?

Unless you couple that with a battery. Then low and slow wins.

That's a strange lunch your cooking up.

Here's a few things to read UFH-System-Design.pdf UFH output calculation.pdf

If they are quoting a buffer it isn't an expansion vessel. A buffer requires secondary pumps, a volumiser doesn't. A buffer provides hydraulic seperation and therefore needs a pump(s) for the heating circuit. Samsung Gen 7 schematic don't compel the use of a buffer, if your are doing an open system. They show a volumiser on the flow to heating circuit. Cylinder size is basically worked out as follows, 45L per bedroom, plus 40L. Reheat time assuming 300L and a 5kW output will be around 1hr and 20 mins to 50 degs, assuming bulk average temperature is about 30 degs.

Out of the parties that doesn't agree has the design flare? They are right. For me it's my wife, I have a say, then I'm told what going to happen. Simple.

Generally never required with sensible design. What size? Good. So basically the design should look something like this. Two floors if the same design flow temp no mixing should be needed. If one floor needs a higher flow temp some mixing may be required, this should be fine with an electronic mixer not a mechanical one. But if well insulated upstairs should really need much or any heating. So I would be tempted to flow a single flow temp to both floors and balance as needed with flow rates. So next is system capacity. You will need at least 20L per min kW output of the heat pump. If you don't comply with that add a volumiser on the return line prior to tee coming back from cylinder. Then run open loop from ASHP on weather compensation. Alarm bell - if you are bigger that 6kW, find a different installer. Alarm bell installer talks about a buffer, find a different installer. You want an efficient system you want a heat pump that modulates to at least half your heat loss at -3, then the heat pump ticks away all day at 7 Deg outside and maybe above that. Would suggest you heat loss is is in the 2.5 to 3kW range from what you have said. If so a 4kW would-be good.

Stops it floating away when you screed?

I just used PIR (70mm) didn't bother with the expansion strip. It purpose is to make up the expansion and contractions of the screed, as the UFH temperature cycles. A second (minimal) benefit is a small thermal break, to decouple the floor. I get the impression it's for retrofit applications where flow temps can be high.