JohnMo

Sorry no vid, not much sun here for the last few days, so diverter isn't having to work very hard. Once you go over a couple kW the fan kicks in Photo attached

You should get a credit and debit for the MVHR on an EPC. It should take the manufacturer declared efficiency, specific fan power, duct type etc all into account. You then get a revised down ventilation heat loss and a revised uplift in electric usage based on the specific fan power.

Running weather comp will not help if you leave your system full of thermostats , the zone size is what is causing the issue, as you describe yourself, kitchen only, an issue, kitchen and living room on together no issue etc. You may be better merging the UFH so it acts as one zone, i.e. drive the loops from a single thermostat. The same with the radiators. So you have only a couple of zones. You will need to balance the system flows afterwards, to get an even output from the loops and radiators. By the way your plumber is speaking nonsense. If you are plumbed as an S or Y plan, you will not be able to run weather compensation, as it will reduce the cylinder reheat temperature also.

Not sure on the dip cause. Without battens 2x3/4 would be better.

Asked the manufacturer and the installer password is 195

Neither really deflects under foot, so generally. Not had the UFH heating on for long enough to an idea of feel of the floor from that perspective.

Some feedback as we now have the finished floor finish in place. Reminder of floor build-up Council concrete paving slabs (3' x2') bedded on 50 to 70mm concrete 50mm EPS70 DPM 100mm EPS70 in two layer with staggered joints 50mm EPS UFH profile boards, with 50mm battens at 400mm centres in between and a perimeter batten in 50mm. 2x 9mm OSB (staggered joints and fully glued) screwed to battens Due to the floor not being perfectly level (low spot in middle of floor), the floor was topped in a fibre reinforced self levelling screed, with a max depth of 10mm down to nothing. Thin foam underlay and 10mm laminate click and lock flooring added. Floor feels solid with a little give. But is a little softer in feel underfoot to our 100mm concrete on 200mm PIR, with a 20mm wooden floor bonded to it, in the main house

So if you do lots of frying Don't let airborne grease anywhere near your MVHR, as ducts will get coated and dust will stick etc. They will get clogged. Your kitchen extract needs a grease filter in it and it needs to be cleaned often. Your cooker hood can be either extract or recirculated - your choice. You need to read specs, grease filter performance varies hugely from about 20 to 80% efficiency. Recirculating you need a carbon filter to capture smells, get regeneration ones, wash frequently. Good cooker hoods are expensive, you also need to read the instructions for install as they have very specific height requirements, most fitters install way too high, distance from hob is critical to hood performance, too far away they are all rubbish.

That's great if your in an area where the smart meter works. We have a normal smart meter it has never worked and cannot communicate, as no signal available to communicate through. Back to the topic PV?

Running UFH from an ASHP shouldn't be expensive in fact it's possibly one of the cheapest forms of heating when coupled to UFH. Low flow temperature leads to very good CoP. Attached is section out of our technical manual which gives, flow temperature, heating power and CoP, for reference. By the way you should be adding way more insulation, I doubt you even meet building regs minimum requirement, with 100mm. For UFH you ideally need around 150mm or more.

Install 3x more than you think you need, may waste some energy in summer or looking another way give your local community some free green energy. But will have some to use in the winter. Lots of solar and ASHP, maybe an electric vehicle it not convinced yet.

Had a similar issue with mine sometimes working, other time lights flashing randomly or going into heat protection mode at 8am, when next to nothing being generated by PV. So just bought and installed a Cool Energy PV diverter. It actually tells you what's going, how much energy is going to immersion at that point in time and over the day etc. You can also set immersion boost times if you need to. It also has an internal fan to keep it cool. Only downside is it has a fan and it a little noisy.

Still not cheap and only a 150l cylinder, so not the best for a heat pump

Plus you can pick up a heat pump for the same or less money than a heat battery. Why not connect to the oil system, you already have?

And why would anyone pay £6500 for a cylinder. Unless as @Dave Jones says. If you really have to go pre plumbed go on eBay and pick one up for £800. I have just done a 6kW ASHP install for £2500 (less the cylinder) as I didn't need one.

Section 2.20 says they are in included a heat pump heating water, it is a fixed unit. So should qualify. But has to be purchased and installed as a single transaction. So if the plumber isn't providing the cylinder you need to pay Vat on their bill.

Interesting I did get a quote for a Dutch system, that had limited inlets, but you have to be clever to ensure you get flow through the dry rooms. For interest I have attached the layout for our house. I didn't go this route in the end but used coanda effect supply nozzles, which does limit the duct lengths considerably.

That'll be right, you hold it she tells you what you are watching, you fiddle with the controller.

£10k is with the grant. I have just completed a DIY install 6kW ASHP, didn't need the cylinder, everything else was around £2500. There are cylinders suitable for a heat pump for £800 (250l) on eBay, so a grand total of £3300 with some shopping about.

Believe you need to be G3 certified to sign off an unvented cylinder install. You can do most the work yourself, as long as you can suitably certified plumber to sign it off. So no idea why you would want building control involvement.

Put some polythene over the top, as concrete reacts with the aluminium

Update After getting lots of other jobs done, got back to the ASHP install. Ended up spending about £2500 all in. I didn't have a cylinder to purchase. Basic description of the setup. From heat pump to house is run in 28mm a mix of copper and Hep2O. The summer house is about 8m from the 28mm pipe run and is run in 15mm Hep2O pipe, the UFH has 2x loops 50m long each. This system has a 2 port valve that closes on a DHW cylinder call for heat and when thermostat in summerhouse is hot enough. The summer house is not setup to call for heat. Once the 28mm pipe gets into the house it is reduced to 22mm and via a 3 way diverter, goes to the UFH manifold where it is distributed around the house via 7 loops. The cylinder is fed via pre existing 22mm Hep2O piping originally installed for the gas boiler to UFH manifold these pipes are around 8m long. Calculation shows the pressure drop for cylinder heating are way to high. To fix this I added a pump in to the return pipe from the cylinder, the pump is powered on, at the same time as the 3 way valve is powered to move to 3 way valve to DHW heating. It seems to work and gets the flow back to 1m3/HR. Had the Maxa heat pump running today. Very quiet in operation, have set to run on WC, and it is basically running on min temperature of 25 deg. Also tried it on cylinder heating, the heat output slowly ramps up until it get to 60 deg flow temp, after this it shuts down. Have set up to run without any pumps or mixer valves on the two UFH manifolds, one in the house and the other in the summer house. Bit of fine tuning to do tomorrow. And loads of pipe to insulate. Photo showing the return DHW pump set up, pump temporarily propped up in a surface mount switch box. Wiring to pump and 3 way valve needs to be clipped in place tomorrow. UFH wiring centre is no longer used as the house is run on a single zone. The thermostat controls the heat pump directly.

The original design by architect and structural engineer had the framing of the windows and supporting the roof in wood, the posts were huge and ugly. Challenged the design, and it came back in 200mm box section, so calculated what was needed and challenged again and ended up with this

That's a quick rabbit hole to close - no PV generation in winter is pants. About 10 to 20% of summer performance. Spend on insulation