SimonD

That limits the options to about one. Although the Ideal thermostats are actually black on the face, but unlikely to work for you. What ASHP do you have and do they not have integrated controls? There is a tendency for some European controls to default to on if there is a problem, either with connection or batteries. The Viessmann controls do the same as they say this removes the risk of freezing if there's a control failure. So first I'd suggest the controls supplied by your ASHP manufacturer. Another, although not in black are the EPH CP4 controls as they function without internet connection and you can buy them with or without a wifi hub. The EPH controls can integrate with weather compensation curves etc. but it entirely depends on what you've got. For UFH you've got Heatmiser which it seems pretty much every other UFH supplier uses/copies under white label.

Are any of us when we start out on a self build journey? Thank goodness for BH where we can dispense with worries about our incompetence and ignorance to ask stupid questions and get sensible answers I say ☺️

Spray painting is great, I love it. But you need to mask everything up properly against overspray and spray mist. This takes time. You also need to spend some time with each type of paint you use to get the settings right through watering down the paint to ideal consistency and then the sprayer so you get a nice consistent spray. Both are worth it in my view as it ends up saving a lot of time. I've found my sprayer and paint (clay paint) finishes with a slight texture so no need to go over it with anything.

The boiler is essentially dumb and slow to respond. It measures just flow temperature so by the time the return temperature has reached the point at which flow temperature increases the heat is already in the system, so there's always going to be some intertia. It's not sensible from a design perspective to make the system respond too rapidly as that affects operating efficiencies and can cause various unwanted attempted control oscillations within the system. The real issue here is that the focus at the moment is only on the boiler and not your controls together with your boiler. At present, even though they might call it a smart thermostat, it's actually pretty dumb because the Hive only provides relay control of your heating. To get this boiler modulating properly in relation to room temperature or outside temperature you need some decent controls that actually modulate the boiler - so either weather compensation, or if you want load compensation, something like the Worcester Easy Control which uses EMC Bus to communicate with the boiler. You can use Opentherm to do modulation, but only with a third party translation kit that you need to get from Europe. Get yourself some proper controls and the boiler will behave much better and can be refined from there.

You have a UFH system that appears to be based upon flow/return temps of 45/40 with a total output of 8.3kW versus your heat loss of 3.3kW. Your heat pump supplier is then suggesting a flow temperature of 35C which would overheat your house with the current UFH design with a 5kW heat pump and you have selected a 300l dhw cylinder. You don't seem to have been informed if this 5kW output of the heat pump is at design outdoor temperatures, or the implications of the large cylinder and heat up times with the current proposed heat pump. And then not to mention the proposal for a buffer and secondary pumps. For the actual UFH output there does need to be a calculation based on proposed floor coverings as they have such a large impact on the system output - one of the two companies should have had this discussion with you. I'm also curious about the figures given in the UFH design tables. For example, your dining room says the ouput is 660w with 150mm spacings and a length of 92m and flow rate of 1.9l/m and your entrance hall/wc has exactly the same output but with almost half the loop length at 57m and exactly the same flow rate. I would expect to see some variation in flow rate and/or output with loops that are so different in length but have the same spacing.

If that's the case, then your output from the UFH needs to be around 21W/m2 assuming the 158m2 area is floor area. Very roughly, in screed UFH would output this at a mean water temperature of around 27C or a flow temperature of just under 30C at outdoor design temperature - this would vary depending on actual buildup and floor coverings, like if you decided to have carpets and wood floor etc. Do you know if any of the designs took into consideration the floor coverings you have? And do you know whether you have an in screed ufh throughout the house on both GF and FF? If does look like you have a situation where the design doesn't quite hang together based on the information we have. With your DHW, as @Nickfromwales and @JohnMo have pointed out, your heat up times with the chosen cylnder could be quite long depending on usage and this is something you need to discuss with the designer/installer to get the system sized correctly to work for you.

Of course. The index circuit is the part of the heating circuit that has the greatest pressure loss. So each meter of pipework, each fitting, like elbows, and for each valve the water in the heating system flows through there is a loss of pressure due to resistance. If you start at the outlet of the primary circulating pump of the system, often now inside the heat pump itself, you will have an available head pressure (usually specified by the manufacturer where they often provide graphs for how this changes according to flow rates) and this is what is gradually lost as the water travels through the system. The index circuit is just the total length of pipework that has the greatest resistance. Once this is known, you know whether the pump for the main circuit produces enough pressure to supply the heating circuit at the required maximum flow rate. This is what should primarily tell you if you need hydraulic separation and secondary pumps. The total resistance of the circuit is done by calculating the total heat load that is carried though each section of pipe from the heat pump to the end of the circuit along with using pipe diameter and resultance resistance of the pipe together with fittings. This should be done with every heat pump design. Yes, these are useful. There are already some discrepancies here. Earlier you said the design temperature of the system was a flow of 35C but the data re the ufh loops says the design temperature is 45/40. The tables each state the output of each manifold, being 4kW and 4.3K which is obviously more than the 5kW unit. I don't know the Samsung units so don't have the technical specs but you need to know what the heat pump is capable of outputting at your outdoor design temperature, which should be given in your design from the heat pump supplier. The tables suggest, I assume, that each manifold has less than 25kPa pressure drop across the manifold flow and returns whcih equates to about 2.5 meters head, but nothing more specific. However this can be calculated more specifically as the relevant data is there in the tables. What is the estimated heat loss calculated for your house?

No, not your fault at all. The ASHP supplier should be doing at least a basic calculation of the index circuit of the UFH as that will help them to design the ASHP system properly. But I assume from what you say that the people who installed the UFH have installed just the UFH manifolds without mixers and pumps on the manifold? Yes, absolutely. The simpler the better, but for a 3 bed house, there should be no need for any hydraulic separation or additional pumps with a system that runs low flow temps straight into the UFH.

Yes the addition of the secondary pumps indicates that it is a buffer. I'd be curious to understand what the designer's pressure loss calcs are for the pipework index circuit (the circuit with the most pressure loss)and whether they're worried the heat pump has enough residual head, whether they've specified the buffer because of different flow rates between gf and ff, or whether they haven't thought much about it at all and/or are compelled by some manufacturer requirements. Although 102l open volume is okay, I would personally look to add in a 50l volumiser on your system at least.

Octopus is measuring input gas rate, you are measuring/assuming output. There will always be a difference between these as your boiler will not run at 100% efficiency. With zero heating controls, efficiency of a modern boiler is assumed to be 89% in testing and depending on the whole system could be as low as 75% efficient.

Yes, they're part of the same group.

It may very well continue until flow temp starts to increase due to increase in return temperature. As you don't have modulating controls the boiler will modulate only on its internal temps. Glad it got sorted. The behaviour was very interesting.

It would be interesting to see any difference in colder temperatures with greater load on the system, but extrapolationg that 10% over a heating system would be significant. What was the rationale for suggesting a higher DT to begin with?

Unfortunately there doesn't seem to be a completely reliable solution but I have gravitated to always using Starrett hole saws. Just a a few weeks ago I had to make some holes in a stud wall right the way through some 5mm screws. The Starrett hole saws didn't show any undue wear from this excercise. I use the deep-cut version as they go all the way through normal joists etc.

+ 1 I used these when re-roofing our old place. We had a very shallow slope so the increased uplift protection was needed.