JohnMo

It was originally specified based on low temperature heat transfer. It's pretty huge Secespol LA34 40 plate. Used an online PHE sizing tool. It's getting an approach temp of a couple of degrees, with boiler UFH and similar when doing DHW heating. Few trends below, first is boiler flow temp and cycle temp - using phe and heat pump cylinder. dT does decrease as cylinder gets hotter. But boiler seems happy enough. Second is a typical run on a cold day, the bouncing about between 1 am and 3 am on second trend was heat pump also running. The spike is DHW heating. Third trend is a start and run of just the boiler doing UFH

Why do an ESBE? They seem well engineered quality valves https://esbe.eu/group/applications/underfloor-heating#underfloorheating

Zinc roof are or should be zinc, not galvanized steel. So shouldn't be an issue.

We have a larch garage, they insisted galvanised nails were fine - black streaks everywhere 3 years later. Company disappeared. If it isn't good stainless, do good plastic. You won't look at it month after installed. Powder coat is pretty rubbish, stainless screws will make contact with carbon steel and cause corrosion - black streaks. Aluminium may not last long especially if coupled with stainless fixings you may not get black streaks but the aluminium will be eaten by stainless.

Would say you need them in both rooms. Building regs give minimum flow rates required in every part of the UK. That or nice mouldy windows etc in a few months of use.

Depends if you ask, depends if you have a main contractor. Main contractor my tell you to get out, depends on the agreement in place

Generally the cheapest overall would be plenty of solar, battery and heat pump and delete the boiler, no maintenance or standing charges for gas side. Both charges out way any of the saving made on the cold days even in NE Scotland. Getting the diverter to ASHP to work outside home assistant, with standard stuff and no need for internet, would be good. But no idea how to do that.

I have the luxury of lots of concrete in the floor, so that will buffer loads of heat. Generally without over heating the house. Once heating is off, cooling generally goes on, so have to be little more careful with that. So will not be charging the battery fully overnight, so PV spends more time battery charging than anything else.

Pod - my summer house (heated all year) CCT - close coupled tee ASHP, can run two temperatures, set via a zero volt contact. Shelly relay is used to switch between the two settings. Shelly control is via home assistant, it monitors battery state of charge and PV output. So if battery state of charge is above 97% and PV is generating more than 600W, ASHP runs and stays running until battery drops to 95%. Have a similar setup for the immersion. Idea is I never let battery get to 100% charged and export little or no electricity.

But still electric is as high as ever. With a price rise of 6.4% in April.

OP has ALL set to 23. Isn't the idea of WC you balance energy out with energy in. TRVs are limit stops not permission for boiler or heat pump. TRVs just fine tune balance as required. Need way more information

Easy peazy - Vertical panels spaced to get tractors and implement through. Do it Japan and other places, so why not here? Almost zero crop loss. PV density not that great, but you can do over 1000s of acres.

And there are Scottish parliament ones and UK ones, so two in each area. Same in Wales also.

Not something you want to do, or need to do, 16 to 18 is fine for UFH (cooling) If fan coils are sized for heating at low temperature they are huge capacity wise, so warmer temps for cooling is quite ok as well.

It can have both, but OP is using thermostats for a heating system run permission to get WC on via ASHP and by default an oil boiler on also. If oil will do similar WC curve great, if not it will just heat whole house to 23+. Which is possibly the reason for the question. Fine if you like a 23 Deg house, but uncomfortable for me.

Heat pump isn't switched off fully the compressor is. All heating control is still heat pump. Your issues are likely to be Heat pump has a run permission from the third part Wiser system. It normally runs WC so I assume the Wiser system always calls for heat? If your WC isn't carried over to the boiler it will just fire away until ALL wiser thermostats are above 23. You need to decide if you are running WC or thermostats! Have a think and report back?

Just looked at 12:56, our generation mix is 77.3% wind, and 22.7% gas. Yet the whole price is governed by gas wholesale price. It's a scandal. +1 Too many NIMBYs, with too much say... But not enough education to have a voice, in my humble opinion. Fill all available landscape with wind and PV. No issue with farmland sharing with PV, they can coexist in the same field.

Today has solar excess so floor is being buffered from heat pump. So unlikely any additional heat will be needed overnight. Average heating cop is 4.47, but as day temp increases, the CoP also goes up even with rising flow temp.

Way more info needed

More an experiment to see what I could do with a boiler, that was almost new and just sitting there - not wanting to give it away, really. 5 degs was the lowest temp I could set the controller to to enable heating. But we aren't that far from the coast and can get defrosting at about 5 degs. When we get defrosting CoP drops to about 3. We pay 13p overnight, so about 4.3p per kWh (0030 to 0730), gas is 5p and not quite 100% efficient, so pretty much like for like pricing. But once a sustained below zero the heat pump runs in the expensive period (0730 to 0030) at 30p, so getting towards twice the price for electric, compared to gas for the same kWh delivered. So overall a little cheaper, but not much - if I had to pay for hybrid system not really worth it.

@Roger440 Sorry for the delay forgot all about the schematic. Seems to work well 5 degs and below for at least 6 hrs, is needed to allow the boiler to run. All other times ASHP runs. ASHP set up via Home Assistant to take excess PV when battery is above a set charge and generating enough PV to get a decent run time. Past few weeks nearly all heat pump running has been on excess PV - so zero cost, boiler had no need to start because house was warm enough. No excess solar yesterday and down to 1 deg overnight. Heat pump ran for about 2 hours and the at first defrost, the boiler picked up the drop in flow temperature and started up, it did the rest of the heating overnight. Heating Layout and Control.xlsx

Lowara Ecocirc pro. It also has the thermostat mentioned by @joth built in, which is adjustable.

Ivar Unimix. Way better than most tat on the market. Has adjustable primary by pass to ensure heat pump min flow is always achievable, plus a secondary one to adjust how much mixing occurs between incoming water and return water.

Doesn't really make sense for cooling either. Heating and cooling are very similar, low and slow for heating gets best CoP, warm and slow gets best EER. Just use a flow temp about 16 degs for cooling, use floor as your buffer and let the fan coils tick away. Flow 7 dags at 30 outside gets an EER 3.7, while at 16 you are getting 5.5. Push the flow to 18 get an EER of 6.2. Getting close to half the running costs of 7 degs - zero condensation issues, heat pump ticks away, nice and happy. Add some PV, it does it for free - or near enough.

No - keep it to a simple timer