JohnMo

First sensible and clear answer - well done.

I wouldn't get to excited - that's a cold water storage cylinder, for rainwater etc. Not a buffer being discussed here, very different things.

I would concider corded as well. Personally if I'm using angle grinder I do a lot with it. Corded are really powerful last as long as you mains or a generator kicking about. I also prefer a fixed speed,with a sliding on or off switch. It all depends on what handed you are, you will hold the angle grinder differently. Don't try to force your self to do it wrong, it will end up hurting you. Also safety glasses are a must, anyone why says otherwise ignore them. Been to A&E several time after doing a quick job and getting stuff in my eyes.

Givenergy all-in-one is an alternative to Tesla, I am paying a little over £1k less including vat, fully installed. DIY on £9k is a lot of panels, mounts and inverter. A panel around £100. Best place to install is the place with the least shading at time of the day, summer and winter. Mount angle closer to vertical is best for winter production, at the expense of summer production (when you have loads anyway) close to horizontal is best for summer, but almost kills winter production. I have one array at 45 deg, fairly balanced, the other vertical for good winter production.

You have a modern well insulated house, your flow temp most of the time should be flowing sub 30, closer to 25. My heating curve is a flat line of 26 degs until 9 deg average outside temp, the flow temp then rises to flow temp of 35 degs at -9. Most the winter should be sub 30 degrees flow temp.

Engaged water is the quantity of always open to the heat pump circulation pump. So basically open loops. Doesn't matter about maximum. 35 sounds hot I would only be flowing that at -9 and I am on 300mm centres. If you are not loosing enough heat, that is simple, you are flowing too hot or you don't have enough heating system engaged to absorb the heat. Turn down the temperature, or make circuit open at all times larger. Basics Heat pump flow temp is set by your setup either fixed or weather compensated. The delta T is also pretty much fixed. That will be in region of 4 to 5 degs. Heat pump gets a call for heat, circulation pump starts, heat pump reads the return temperature and adds heat inline with the pre defined Delta T, as the heat is absorbed into the floor or room, the delta T will drop, so the heat pump adds more heat. It will continue doing this until it hits the target flow temp, plus a small amount (0.1 degrees or so) it will then shutdown the heat, but continues circulation. Once the return has reduced to a defined level maybe 5 degs below target temperature the flow heating will resume and keep repeating this pattern until the call for heat is cancelled. The more system volume and house available to absorb the heat, the longer the process between cycles takes. The process should take a minimum of about 10 mins for the heating cycling. Depending on the heat output versus heat required, the off cycles could be very long.

I did mine the heights of COVID when everyone was working from home, possibly they had nothing better to do. Plus the architect did the first submission, I just picked the pieces, "if want something doing right, do it yourself"

Would it cheaper to run the immersion on a Sunday morning to charge the cylinder to higher temp - more capacity sorted. I am assuming your on a heat pump?

Sorry just read the first post again, you do need SEPA approval to operate, the full design has to be approved by them, including make model and size of treatment plant, soakaway design etc. They will question everything we got questions on loads of stuff. https://www.sepa.org.uk/regulations/authorisations-and-permits/application-forms/small-sewage-discharges/

I did the water regs course as well, that was included.

I had a Ivar mixer (tried a couple of different ones), you cannot close the feed of returns water to the feed water, no matter what alterations you make to the settings. So if your UFH flow temp at the manifold is 30, your feed to the mixer could be in 35+ range. So you instantly get a CoP hit.

UFH in bedrooms is just wrong, we have it, basically just switch it off (well circuit is actually on, but heat output minimal) as either to warm or not warm enough, cannot control it as the lag time is massive. For the times you need heat, an hour in the morning a couple at night, a panel heater may be the best solution, with a timer and thermostat. Wet rooms upstairs dual fuel the towel rail, and include UFH if you like. You then keep the heat pump installation really simple, one flow temp, one zone. DHW is treated differently from heating zones by a heat pump already. If it gets a signal for DHW heating, the complete operation strategy changes on the heat pump. Circulation pump runs at max fixed speed, it does not modulate on mine, mine will not defrost in DHW mode, for best CoP temp rise is slow from the heat pump.

I know Daikin do an ASHP specifically designed to be installed with an existing combi boiler. Boiler does DHW and heating. But heating can be done by ASHP only or mix of gas and ASHP or gas only depending on energy cost and CoP of ASHP. There are lots of advantages to a hybrid system, basically very little plumbing or radiator changes. System runs on weather compensation, it's only when temps get close to zero that the boiler kicks in. You don't need a cylinder, which can be a big issue in a small property and ASHP can be tiny.

Must say have lived in dry lined walled houses for over 30 years, and poor durability of the plasterboard has never been an issue, I have witnessed - in my house or anyone else's. Been used in England since the late 70s I believe, but mostly in a commercial setting, where if it wasn't durable, that would be more an issue.

I paid just over £500 just a single payment for everything (I hope), which was more than I was hoping to pay. But on doorstep, so to speak. No teaching so to speak, basically here are the regs, logic training notes on DHW , cold water and heating systems. You sit two (might of been 3) multi choice paper, plus two papers where you have to identify parts of the UVC control system by photo and then again by description of its operation. You are shown photos of key areas of the system and have to highlight the things that are wrong, then by description do some fault diagnosis . Then describe the things you look for on an initial survey, how you commission a system and the maintenance steps. Pass mark for all tests is 100%. You take as many tests as you like until you pass. Water regs are similar format but pass mark is 80%. I was there from 9am until 3pm incl an hour for lunch. Some apparently take 2 to 3 days.

Not really that necessary for 100mm centres if well insulated, I am running 300mm centres, max required flow temp is 35 at -9 outside. Really if you match the rad size and the floor centres so they all have the same flow temp on paper, you can then balance the flow rates to get the room temps where you need them. Then you are running at the lowest flow temp. Then you start questioning the need for any mixers or additional pumps.

You get it easy in England, in Scotland we have to design the whole treatment system, with all supporting calculations. Get a licence from SEPA to install and operate and it has to be installed per design and any additional stipulations made by SEPA. In England it seems you are able to design (maybe too strong a word -knock it up) as you see fit - right or wrong. Prefer the Scottish system, it's black and white (ok or wrong)

I have two units, but that's to do with our house layout and the resulting duct lengths. My whole system was under £2k installed. I like Titon HRV, UK made, good tech support and spares on the shelf. Often come up on eBay for super cheap prices.

Get the manual out, if a proper hybrid install there will be an algorithm in the controller. You basically input the tariff info for gas and electric and it sorts our when to run, based on the cheapest for the end user. Combi boiler?

Looks ok. Couple things to consider, cylinder heating time, that needs to added into the mix and possible defrosts. I have a similar heat load, a 4kW is a little tight on capacity, so I have a 6kW (super cheap, very efficient), but as @HughF say a 5kW is fine also. You just need to ensure you have enough water engaged to stop short cycling (about 50L).

Does it have humidity sensor built in?

I would temper that with, a remark on noise and overall reliability. Also support and spares if things aren't quite right. I bought my units from eBay but expensive units for super cheap prices. One unit had an issue, got great support from Titon and had the spares in two days. Set it up per building regs then once signed off, used the setback setting, which knocks fan speed down to between min speed and current speed setting. Rarely use boost, totally silent, zero drafts, monitor CO2 in master bedroom and lounge - zero issues. Runs 24/7, nothing smart, manual boost switches. Complex controls if you like, but no need.

I just rang the college, if they do plumbing, they will do the course was my thoughts. Would expect the college nearest to you will do it.

We had an expensive one in the last house, it was rubbish and started dripping after about a year, spare part prices were stupid prices also. It looked nice, but that was all

Yes, but no idea how long my ticket lasts, but I would assume having a ticket makes me competent to do annual checks for ever. Won't bother asking the question. Yep. Did it at Moray College in Elgin.