JohnMo

Correct

When on cooling mode there is always a slug of cold water that gets sent to cylinder coil. Not much different to the ASHP being off, the whole pipe contents will have cooled down to atmospheric temp. So a call for DHW heating then a similar slug would also get sent to the cylinder. Nothing clever seems to occur.

That would be it, (not checking what I'm typing)

Decent deep fill filler, couple of coats, deep fill to fill the gap and the second a fine filler to take up the shrinkage. Your terminal will cover it also.

MVHR is just ventilation, leave it to get on with ventilation, no heating or cooling coils, they work a bit, but not really worth the faff and huge cost. Solar PV, again pretty much leave it as stand alone, ASHP and MVHR will naturally use any electric before it gets exported. Install a diverter to immersion if you don't get paid for export. ASHP leave it to do either DHW or heat and cool via a 3 port diverter. That gives 3 stand alone projects, nothing is lost in translation, all should be pretty basic installs. And everything @Dave Jones said.

As promised - system layout and control. My DHW is a bit more convoluted than normal as the cylinder is remote from everything else and needed an additional pump, so hydraulically separated via a CCT Heating Layout and Control.pdf

The white one is for the cylinder. When was the last time your cylinder was serviced? You need to be competent to work on unvented systems and they should be services annually.

Will go on to the computer tomorrow and add a copy - has all the settings etc

Correct My automation is simple - the wife says for for a day or two "it's cold/hot isn't it". Flick summer winter switch, set thermostat to heat or cool. Takes about a minute twice a year - not worth the effort to automate. Trouble with automation you could get into heat cool ping pong without realising

It's taken me a year to get there!

You can and mine does it all the time. I run pretty much pure weather compensation so the heat pump is energised and ready to go and circulation pump on all the time, except 1. During cooling the house drops below 20.4. 2. During heating the house goes over 23.1 A thermostat stops the cooling or heat demand. During cooling and heating I have the temperature settings set, so they automatically modulate the heat pump output to match demand. So in cooling when the house is sitting at about 21 the heat pump compressor will run for about 10 mins every the hour or two. When the sun's out and we get plenty of temperatures rise, the heat pump compressor can run 40 mins an hour every hour. All done by the heat pump sensing the return temp - the restart hysterisis of 4.9 for the compressor and flow temp target set to 14.5, so when the floor goes above 19.4 the ASHP compressor starts. Heating is done in a similar way. The continuous circulation helps even room temp and gives the fan coil a flow of cool water for continuous slow cooling effect.

Not really. The cold main is connected to the inlet group of the UVC, which is connected to the bottom port of the cylinder. The expansion vessel is connected either to the inlet group or cylinder contents via a port. So a closed main valve. A collapsed or punctured membrane on the expansion will alter system volume/pressure very easily. So worth checking. Also check the tundish at the UVC for drips. Good sign something is not right in that area could be a passing valve?

They are normally for metal, the wood ones are very coarse thread

Check the unvented cylinder. There is an expansion vessel for that. If it has lost pressure that may cause the issue.

In the heat pump, just a single circulation pump. Everything run as a single zone or DHW heating.

Then do this. The rest is just a waste of money. So basically convert combi to system boiler, so in summer during a warm dull day (not much PV) you have to fill a big thermal store with hot water to enable you to have a short shower? Why?

That looks a complex system. What system is loosing pressure The main water The heating system or the unvented cylinder?

I would be very careful about going complex. All sounds great until it doesn't work or never works as you think it should. Issues are some manufacturers of combi boilers allow pre heated water most don't because they are not really sure about it. So their easy answer is no. PV and battery, let the PV charge the battery. Use the electric as you need Really would not bother with the complications of a back boiler. Why, you now have a combi boiler doing DHW and doing CH, you have a cylinder you have to charge up to get CH started, this could be heated via combi (via a coil as combi's need a sealed system) or heated by back boiler. Your cylinder will be a thermal store and really need to be pretty big if coming off a back boiler. Bucket loads of heat loss as it will be vented and get to high temps. Companies will do an integrated system and charge a pretty penny for their troubles. My view your heat loss / waste will be pretty big. I would Small wood stove if you must. Spend the money or most likely just time to get weather compensation working on the combi. Take as much gains in efficiency from condensing as you can. If you combi will take preheat, a small 50L cylinder is all you need. see attachedCombi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf Leave a few thousand pounds in the bank. Save money every day of the heating season.

Work fine for us, but we do cycle on the heat pump (it's too big) so average is possibly closer to 16-18, depending on solar gain.

Fan coil is similar to the heater in your car, a heater matrix and fan to blow air through the matrix. The water can be a fixed or variable temperature and fan speed moves to get the heat out of the heater. In cooling mode you supply with cooled water and it blows out cold air not hot.

But that is only really true for the first heat cycle, after that it's only heating the bottom third in reality. My 210L has never taken more than 45 mins to heat with a 6kW. Look at the many threads on different forums where cycling is an issue. You can manage cycling but it doesn't generally happen out the box. Certainly not as left by many installers. Samsung requires use of the controller thermostat and water law together, to add more hysterisis to the heating system, mine required the hysterisis setting moving a long way from manufacturer setting, some heat pumps use good controls that make sure cycling is acceptable as a default setting - many don't.

Sorry to be blunt, that kitchen looks boring. Get yourself to a decent kitchen designer. It's in the living space, you need to think of it as furniture. Things I don't like, kitchen units finishing part way across a window, looks naff. The area where the hob is really needs to be tall units, and incorporate your oven, microwave etc in there. Your fridge in a different colour looks odd. Assume it's a stand alone, not integrated?

Think that's where it all started from, but believe it's been distilled down to energy meter - but not really true for any more for heat pumps - as even a leaky shed could be Passivhaus with a well designed ASHP system. So think it's really delivered heat now.

Should be ok in a partition wall, that isn't structural. Not many screws are classed as structural, so you should discuss with your structural engineer what to use. The size will also be very different from a nail due to the physical properties of the metal used in screws and nails.

Because it can't do it very well and it isn't cheap. I worked out our near 200m² house on normal MVHR flow rates, MVHR colling would deliver around 1kW if heating. The ASHP flow temp was 7 degs. Our floor can deliver 4x that at 14 Deg flow temp.