Nickfromwales

Yup. Definitely a waste of time and money. Your boiler will be chucking 30kW in and another immersion would only provide another 3, totally pointless. 100%, dress or no dress.

Every bit of info I've had, even from the various manufacturers own tech / sales people has been so unclear and indecisive that I instantly removed myself from a position of quoting for such a system to a client who had expressed interest in one. I was being told of "how good they were in Japan", and thought...…"but I'm asking about the UK you nugget ?!?" I'm all up for tasting new flavours, but this one went sour pretty damn fast. If you don't want to ( simply and relatively cheaply ) boost by electricity then go for the hybrid. PV would swing it to the electricity option afaic.

Be good if you have as you'll have a separate flow tapping for the DHW PHE. With regards to sustain, I wouldn't worry about sapping the cylinder as the space heating wont even blink if its has an empty buffer for 30 mins or so. Only issue will be the useful temp cut-off point of ~40oC but if you set the cylinder set temp to ~65oC and try it I think you'll be fine. If your DHW usage is higher and you find yourself needing more 'capacity', just incrementally raise the set temp by 2oC and retry daily, adjusting accordingly as you go, until your happy.

Just enough time to try all your frocks on Images I cannot un-see

Do you mean it has an auxiliary tapping 2/3 of the way up on one side ( which is a hot return tapping ) ? A regular cylinder has cold in, side mounted at the very bottom x1, combined hot and vent out of the very top x1, and nowt else other than the coil tapping's which are hydraulically separate.

So, to clarify, your cylinder has the 4 individual tappings as shown, plus the 2 for the coil ?

The whole point of the buffer is to allow your big gas boiler to chunk heat into the buffer at the optimum condensing range flow temp. The boiler should not be constantly idling to keep the buffer temp low, nor will it be able to as that model has ( IIRC ) 7kW minimum burner output at maximum modulation. The way you propose to run it will see the boiler constantly cycling, fan constantly spinning, gas valve constantly active etc, so will reduce the longevity of the boiler too. Please elaborate? You'll still need 2-port zone valves on each run to stop flow when not required. If the pipes aren't in yet then just throw a cable in as you go. The kick in the nuts is that you cannot reduce the size of the DHW device if you only have seasonal uplift ( eg the heating is on so you get preheat as a side effect ). Not so problematic if there is enough excess PV to heat the buffer an the SA / UVC but then its just additional summer heat gain, and often unwanted. You'll be there for years trying, and it would be a nightmare to balance and keep balanced.

Yes, noted, but you don't have a mix of emitters over a number of floors. To have one flow temp to all the manifolds with them just having pumps is not a good idea, IMO, given I've done such installs and found it essential to be able to choose a slightly higher flow rate for the UFH over the timber floors, even with aluminium spreader plates. Bear in mind the UFH here is router'd into insulation with no aluminium plates to conduct and dissipate the heat effectively.

We always used dedicated nylon washers for isolation when working on the ships. How reliable / weather resistant is the paste?

Do these things expand / contract at all ?

If you want your pumps and valves operating 60 times a minute then yes. Best get to the NASA boot sale this coming Sunday

There is absolutely no way you should scrimp on having no mixing valves on the manifolds, especially as you'll have different floor constructions. You will need to have a very fine tuneability for the basement and the ground floor, and trying to achieve that with one global flow temp will be impossible. Do not cut corners here. Do not use your potable water TMV for heating, you'll need a Heating type Reliance valve for that, two totally different beasts. For flow control to the manifolds you use the reliance valve and a pump to circulate between the cylinder and the manifolds. You should be fitting a 2-port zone valve to each leg to stave off unwanted convection heat flow and to be able to isolate each leg according to whether or not that particular manifold is being used. If you've already run the 22mm as a single pair then you simply put the 2-ports at each manifold. The cables you require to control these should be found in the manifold wiring centres, if you've fitted them. If not, get cables in now. The UFH temp is controlled by the mixing valves on the manifolds, ( 20oC to 60oC range so very accurate in a PH ), and the flow and return temps are shown on the manifold temp gauges normally. If you don't have them then cheapo Chinese digitals are available or chuck in the thermistors and reference off the HA system. Ok, much to @PeterW's entertainment I am going to retract my statement re deriving anything other than cold mains uplift from the cylinder. I looked at the link and its just a domestic hot water cylinder not a TS so is completely unfit for gleaning various services / inputs to / from. Too many good films on yesterday is my excuse, with 'Where Eagles Dare' being the highlight. With the mention of TS I dropped into default and assumed the coil was a DHW top mounted. Hydraulically separating the UFH from the main body of water is a step in the wrong direction, as you'll not be able to use the F&E tank to service that circuit. You'll then need to fit a separate fill loop, expansion vessel, pressure relief valve and pressure gauge to fill up and maintain pressure in that circuit. Is the F&E tank higher than the upper floor of UFH? Adding a SA seems the easiest way of dealing with DHW as they're compact and don't need an overflow ( discharge ) arrangement like an UVC does. A 6 will suffice if you're heating it from the gas boiler, but you'll probably be better off with a 9 ( £300 more then the 6 so not a great uplift when you look at the incremental price increase ) so you have somewhere to dump PV in the summer ( when you don't want to heat the buffer ).

Do you have a link for the cylinder so I can see the thing in all its glory?

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The coil wouldn't do DHW as it wont be efficient enough at max flow rates. Agreed. That's why its for DHW uplift. Yes, I was watching Iron Man and not concentrating and forgot its not a proper DHW coil in the top of the TS. Damnit !

Ah, my young apprentice...….."the force is weak with you" The PHE would be a hydraulically separate circuit off the coil. The TS would be heated by the boiler on a reversed S-plan, as in the heating would be teed off the tapping's and only drawn off when there is call for heat. When the pump in the boiler runs it will exceed the UFH manifold pump velocity and promote flow without the need for a third pump to circulate between the TS and UFH. Winner winner, chicken dinner.

My statement is for an open pipe arrangement where the boiler doesn't heat the TS through a coil. The coil stays for DHW output and job done. It'll heat fast as fook so no issue if not using the coil for input.

Erm…...the cylinder doesn't deliver the heat, that big white box sucking in gas does Your cylinder could be a 15L low loss header and still provide all the heat your boiler does, because its coming from the boiler VIA the cylinder. As I said, the 140 will do it, but only if the boiler is allowed to replenish heat to it via the cylinder stat. As far as DHW is concerned, if a big boiler is connected to it then the 140L TS will be able to give you constant DHW to 2 showers with ease.

Yup. A couple of decent pics of the threshold junctions please

The 140L cylinder will work, but only if you maintain it at 75-80oC which will be ridiculously high on losses with a vented setup. That kind of flies in the face of building to a low energy standard, so I think I'd look at reverting back to sealed and pressurised in one much larger cylinder and get a G3 sign off. You can go 'all Sunamp' to reduce losses, ( expensive additional costs ), but the header tank will still remain because you bought the open vent boiler. Can you get an MVHR extract duct to the location of the F&E ( header ) tank? May as well recycle that heat as much as the MVHR will afford you to. edit : the MVHR will also help manage the excess humidity local to the F&E tank, as that may well become an issue too.

Agreed. They seem to have added more problems, by involving the inbuilt immersion heater, that didn't previously exist. Was the SAPV A rated? I cannot recall.

If he's got time to look for £3 showers he's got time to write his own email ✌️ ?

Oh yes, you said open vented not open flued. My bad, scan reading again Classic System aka sealed and pressurised Classic Regular aka 'heat only' / open pipe / open vented Which one do you have?

Ok. There is no way I'd put an open pipe, high temp ( therefore high loss ) cylinder in my new house. Just goes too far against the progression of mankind, sorry. All you need to do here is provide a better medium for transferring PV and gas into DHW, purely because 140L is just under half of the size of TS you'll need IMO. Somethings gotta give, so I shall stick with my previous recommendations, to fortify the existing tank with an ASHP ( only because of PV and the side effect of gaining cooling which is nice to have at the end of the day ) so you can keep that at a lower temp = lower losses, transfer ASHP > DHW to provide much of your bathing at max CoP and from 'free' PV generated electricity where available, thus giving you a lot of very cheap / free background heating and DHW, and retain what you have. The alternative is to bin the 140L tank cylinder and replace with a 350-400L unit which will give much more sustain at lower set temperature. It would give you the single cylinder solution you seek ( and remain DIY ) and have sufficient size to absorb all of your excess PV.

But the bone of contention is still not having an accurate ( actually ANY ) SoC indicator. How do you know how long to boost for? How long do you leave the SA deenergised for before boosting, without running out of hot water? Simple answer is trial and error I suppose, but then there is the question of sizing...…... Paracetamol, anybody?