Nickfromwales

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?

Nothing worse than putting lipstick on a pig Pay for disposal and start afresh. I wouldn't want to spend a lot of time in there tbh with its ( the asbestos' ) integrity unknown.

Hi. Assume you mean to remove and dispose of the asbestos sheets and start from scratch?

Wring them for some vouchers. Reply that you are looking to be compensated for their incompetence in restocking an item that should have gone into the discount bin and sold as parts missing / unknown returns, as you took an unpaid day off work to complete the job. Send it to the CEO, its only going to cost you 5 mins at the end of the day.

I think that flooding the cell with thermistors and getting an accurate cell-wide average temp reading could work well. Do away with the 50/90 setting ( for the PV > DHW model only ) and just have one max threshold where anything at or close to 75oC ( cell average temperature ) allows electrical input. 75oC or above = satisfied. This remains open-ended though, as you really need a SoC indicator to correctly identify if you still need to perform a manual boost or not ( insufficient excess PV in that 24hr period ). Other than that, boost is a guessing game. At least with a load of thermistors the ctrl PCB would have the ability to gather and offer this info to an LCD display, giving the end user at least some indication. With a bit of additional logic and an integral clock, the unit could self diagnose and perform its own boost cycle where it knows it hasn't received sufficient PV input. I imagine SA would reply that you don't get that with an UVC or dumb copper tank, but with those there is no box of tricks actively stopping energy input at any point, just excess PV chucked at a dumb immersion heater that has its own thermostat. I think SA need to adopt that simple approach and bin the complex control logic ( and the not so complex means of temp referencing that they currently are suffering from with the seemingly unreliable 3 thermistors on the daisy chain ). This isn't so much of a problem if SA is an excess only device eg pre-heat to an UVC or Combi boiler, but very much so if this is the only means of providing DHW to a dwelling.

Ok. This is getting beyond complicated. Lets cut through the thicket and get to basics. First off. Have you actually ascertained that you need active cooling or is it a comfort requirement only? If so, my 2 penneth; Keep your gas boiler as backup and add the cheapest ASHP you can get your hands on. ( Also you referred to this as an open flue boiler, which I don't believe it is. Could you please clarify that it does indeed vent to atmosphere via a coaxial 100mm flue through the wall? ) Use the ASHP to provide background heat from PV when required, and to provide cooling when the sun is causing trouble. FYI, you do not drive cooling into a buffer tank, you drive that directly to the slab as you don't benefit from a cold tank ;). Switch to gas when the sun is poor / infrequent so any PV generation goes towards your base loads, lights, plug in loads etc. Best of both worlds then, as you'll be fully utilising PV and burning cheap gas when necessary. I wouldn't suggest this tbh but as you've already gone and bought and fitted a gas boiler its now an exercise to make the most from what you have. I'd recommend just adding a Sunamp, mostly for size but also for simplicity, and feed that with pre-heated cold mains water from the buffer DHW PHE. That way you can use the ASHP to provide uplift, use PV to fortify both the buffer and the SA, you can reduce the size ( and cost ) of the SA, and you can keep the existing buffer tank + PHE ( as I assume these are also already bought? ). You said earlier that you don't like / want and UVC as you wanted this to be a DIY hot water install. WRONG. When you heat a cylinder ( unless its an open / vented TS ) and that cylinder has a volume of 15L or more, it requires a G3 installation and sign off + ongoing annual G3 inspection. Exactly what type of cylinder do you currently have ? ?

Naaah, probably the handset was too big and wouldn't fit between their legs when they were trying to wash their arse crack. ?

I don't usually bother as they have an adverse affect in the winter. Their the crudest of stats and I haven't fitted one for prob over a decade, other than in rentals where the Tennant only understands noises.

You said you opened it and checked Should have gone to Specsavers?

Water would have come out as they're wet tested by QC At least you can wash ?

Not really good enough for PH or UFH afaic. Wiring doesn't affect the hysteresis, it just makes it work

And the symptom of crap room stat with huge hysteresis giving over and under shoot of the stat set point.