sharpener

No, they have a separate export register but AIUI you will have to get Octopus to apply to yr DNO to allocate a separate MPAN to use this. Have PM'd you also.

It would require a lot of things to go wrong simultaneously on a boiler system for there to be a tank full of superheated water. And more or less a physical impossibiity for one with a heat pump. The requirement for two separate thermostats on an immersion heater have more or less ruled that out as a cause as well. It wasn't always like that. Decades ago during the Edinburgh festival a bunch of theatre technicians wondered why there was steam rising from the WC pan in our rented flat. Turned out there was no thermostat at all on the HW tank.

Too right. They are very reluctant to fit or even connect to equipment they have not supplied, citing split responsibility for warranty issues. I had endless trouble finding someone who would install panels onto my brand new Victron MPPT, they all wanted to fit a grid-tied inverter I did not want. And in the end I am not sure I did not pay for one that stayed in their van.

Weather comp (and E7 rates) will see to that most of the time. The 50C is worst case at OAT -1.4C, a figure I think in any case highly pessimistic as we are right on a tidal estuary in the SW.

We have PV, immersion heater diverter (home made), Zappi EV charger and a battery. Pecking order for the PV generation is by default (and is the same for most systems): House loads Charge battery Immersion heater Zappi Export The only time I need to change this is when I need both the car and hot water. Then I turn off the immersion temporarily so the car has first dibs, this is bc it requires a minimum power of 1.4kW. In the afternoon when the PV drops below 1.4kW I can turn the immersion back on and still make use of the sunlight. If I charged the hot water first it would go to waste. My legacy 3.68kW solar inverter is behind the battery inverter so the DNO considers them as one. The newer 3.2kW PV is connected via a DC-DC converter straight into the battery so the DNO doesn't consider it at all.

You might be able to get it out by pulling it tight against the back of the panel, rotating it a bit anticlockwise then pushing it back in for another go etc. Then as @Nickfromwales says you will get access to the whole pushbutton assembly and the flexible pipe. Make sure you tie string round the nut. Then you can maybe see what is wrong with the pb. If fixed you could then glue it back with something like CT-1. My worry would be that the fault is the other end, at the cistern. Which if true will mean you have the problem of getting at that as the numpties have left no access to it. We have a similar arrangement but the entire panel is on plastic hooks and slides upward for removal. Maybe you are looking at too small an area? Just a hope...

Yes. But no more hazardous that allowing unlimited flammable gas into the building via a 22mm dia pipe. Or 240V mains. Or using a cooker. I continue to think that the fuss is overdone and the annual "maintenance" can be carried out by anyone who can follow printed instructions. My disillusion with maintenance contracts was complete when I discovered that if you take one out with BG it does not even include carrying out the boiler mfrs recommended annual service tasks, merely an "inspection". So for example they would not remove the covers to clean out the condensate trap on my Vokera boiler, which does require GasSafe certification. And I bet they do not remove the cartridge on the UVC pressure reducing valve to clean the strainer, or check/adjust the expansion vessel pressure, which should all be part of a G3 service.

My LA goes out of their way to inform you they are quite separate: "Building Regulations - This decision is not a decision under the Building Regulations and the applicant should ensure that all necessary approvals for the same proposal and same plans are obtained before commencing any work on the site. See www.countybuildingcontrol.gov.uk for further information."

Does this mean you had to get a G3 certificate or did you not bother? I am perplexed why there is such a fuss over G3, the requirements are quite straightforward (and explained very clearly in the instruction booklet for my Ariston tank, though it was not installed by me).

The Vaillant 12kW unit is physically too big for the PD route so I have had to obtain express PP. The notice makes no mention at all of either MCS installers or Building Control. The Environmental Officer's internal report says it will be satisfactory from the noise pov without reference to the MCS standards, only the mfrs data sheet (which I provided). As @JamesPa says upthread the BC process seems not to be very interested in HPs as retrofits, though the electrical work must of course satisfy Part P. I got them to add installing an HP to a previously opened Building Notice (for EV charging point) in case I wanted to do (some of) the electrical work myself. A further point is that to give you the extended warranty terms mfrs will insist you use their approved installers who in the case of big name brands will all be MCS registered so in practice you have little choice.

Well this turned out to be the solution. Installer has corrected the heat loss for the room in question and this means a K2 will be fine there, with a worst-case flow temp of 50C which he is content with. In turn this will give us a bigger margin overall and mean smaller rads in other places which family are happy with too.

Interesting point which I had not thought of, as it is an OSO tank with internal expansion space. Don't know exactly what the construction is, I suppose I have assumed that the outlet pipe which physically emerges from the very top of the tank has its mouth some way down inside leaving an air space. Any air which the pump sucks in will get re-injected at the bottom. If the pump flow is too great I can partially close one of the isolation valves on it. As above, the min setting will turn the tank over twice an hour.

Michael Podesta looked at this in his blog and came to the conclusion "it all depends". There's also some recent discussion in this thread demonstrating that the potential savings are quite modest, around 8% even if you assume setback for 12 hours. To judge by the fact that my room stats click on and off with a cycle time of 20 - 30 mins I think the UFH time constants are quite short. Obvs we will not use it like that with the HP, I will have to wait and see how it all perfoms and whether heating the slab overnight on cheap rate is cost effective or not. Given that we typically do not use the living room until late afternoon it may be that leaving it off or on setback until the Cosy cheap window 1300 - 1600 will be sufficient. We will also charge the TS to 55C during that period. Some years ago I put two big rads in the living room as OH does not like the UFH anyway, the rads give a fast warmup to 20 deg and in future will benefit from cheap heat from the TS. Yes it is unconventional but the calcs all stack up. We don't heat the bedroom at night either, there is enough heat seeping up from the AGA in the kitchen, also MVHR. It settles to about 16C which is quite enough, any more and neither of us sleep well.

I thought for a moment you were talking about sucking air in via an open tap. Then I remembered the whole is pressurised to >3 bar anyway so unlikely, pump only develops a head of 1m even on max setting. Don't see any possibility of sucking air out, where would it have come from in yr scenario? All academic as pump will only run while water is being heated and that will be in the small hours so little likelihood of simultaneous draw-off.

Well you seem to have thought about it all very logically so I don't think there is anything different I would propose. Maybe that is some comfort in itself. Having the two systems normally independently controlled and operating separately is sensible inasmuch as it simplifies the control requirements. If there is however some way of linking the F and R pipework, with e.g. normally closed manual lever valves, this might give you a cheapish way of keeping some heating going if one HP breaks down. I can't immediately think how you might configure the sensors though as am not familiar with Daikin controls. Maybe there is some "limp home" mode you can invoke.

Current plan as agreed with Vaillant tech is to program the TS as a second HW tank and charge it in parallel with the cyl (to divide the HP output between the two and hence not have to change the existing HW cyl which is v diff.). This will mean to get HW at 50C I will need sthg like 55 in the coil and hence give me 55 in the TS also. In winter all storage is good as what I don't need in the bedroom rads I can use in the rads in the living room. Yes, in shoulder season I can also experiment with changing the TS to be a heating circuit, which will mean automatic WC is available for that circuit too, with its own time/temp schedule. Controls have a Parallel Cylinder Charging option which allows this to be done at same time as HW cyl if necessary (though CoP will be lower). But 42.5 MWT as designed results in several rads being too large for the space available unless K3. In practice as many have suggested the whole heat loss is over-egged. I am not sure if/how he has accounted for the MVHR though the box is ticked on the Heat Engineer printout. I also know MCS will not allow him to account for the AGA which puts out ~2kW 24/7 into the room below the said study. So I don't expect there will in practice be many days when we need a flow temp of 50 let alone 52.5.

Yes. This pump will move 400l/hr on its lowest setting, which is faster than ideal but it will be in the middle of the night anyway. Plan is to tee off from the outlet pipe and pump into cw feed at bottom. I have seen the opposite proposed, that would surely feed the c.w. straight to the outlets if anything is drawn off . Hence there will also be an NRV to prevent reverse flow through pump when it is not running.

Very possibly if you are willing to forgo some of the cooling. Have seen yr pic of the shell, looks a fantastic project. Various questions occur to me e.g. 12kW is not a particularly big heat loss, what is the total floor area? What is the general layout that explains the 75m distance? Why is the heat gain so large? Can it be mitigated with shading somehow? Is it in the UK or overseas? Do you have an idea for the minimum cooling you would accept? Is the proposed setup divided hydraulically into area A and area B or are the two HPs supposed to work in tandem on a common layout? That would be more efficient as you would have a greater available turn-down ratio and also some redundancy in case one unit breaks. How was the 16/8 split arrived at?

From the other thread I thought you were now doing the job as DIY with a friendly plumber under an MCS umbrella. Will they not allow you to keep the original Warmflow? As I recall it has twin coils which you were planning to connect in series. If you choose the 5kW HP I am sure it would be more than adequate, as posted elsethread it will turn down to about 2kW when delivering at 55C. I have recently had a quote from an (otherwise reasonable) installer who is very keen on the Heat Geek cylinder which is made by Newark. I have looked at this and think it is over the top. Also some of the stuff in the first HG video is IMO plain wrong, I think keeping the tank mixed as it heats up is thermodynamically the better thing to do. Maybe @JamesPa has a view on this? Yes I have read that Joule have poor quality control, and also that Gledhill are not 100% pressure tested at the end of the line with leaking joints being reported on arrival. So I would pick Newark's ordinary range or Telford.

No, it is the 3kW and 5kW that are basically the same unit, the 7kW is different and taller. The 3kW is restricted to 85 rps by the compressor software, this also means that both models turn down to the same minimum output figures so the dynamic range of the 3kW is less than 3:1 whereas the 5kW is more than 4. The Vaillant control system integrates the error term i.e. the difference between the setpoint and the actual temp. I don't claim to understand the detail but I think the settings can be tweaked to achieve what you describe.

Well funnily enough we are indeed going to put a radiator in the en-suite which doesn't have one atm and is freezing cold. And the other cold area is the landing where we can replace the 600mm high rads with wider 700s. Have now found what I think is the big fix. The problematic study had been entered in Heat Engineer as having ground at 11C underneath it not kitchen at 18. That should bring the room heat loss down by 300W which might be enough to lower the required flow temp to 50 which is less of a psychological challenge. Am hoping installer will also buy the argument that the rads will be fed from the TS which will be charged twice a day at cheap rate to 55C, with as @JohnMo says a rubbish CoP. At -2C the CoP does fall from 2.5 to 2.0, but the electricity costs only half as much so worth using such a high temp to maximise the storage capacity.

The HP recommendation from MCS and the tank mfrs trade association is based on 55C IIRC. I don't know what the recommendation is for boilers. Would be surprised if it is more than 60C bc of the risk of scalding. I have mine set to 50 for the oil boiler and 55 for the immersion, so the boiler doesn't cut in if there has been sufficient PV during the day.

For the nom 10kW unit (i.e. marketed as 15kW by AO) that sound power level of 58 dB is 2 dB lower than the Vaillant 12kW, and the sound pressure at 1m is fully 8 dB less. If you believe they are comparable. Maybe it is because it has one big fan not two smaller ones.

Manual is downloadable from the AO web site you linked to. Looks reasonably comprehensive though the two hydronic schematics are pretty basic (both include buffers, and it shows a PHE for the HW not a coil in the tank, I wonder what country/market it is aimed at).

That Hep2O is the one I have got. The back pressure is IMO unacceptable, I have now got it at the bottom of a vertical drop of >2m of 22mm Cu pipe and it still backs up to the tundish. When I have had it apart it all appears clean and undamaged. I test the relief valve at least twice a year when I reset the timers in the a/c, as upthread I have otherwise stopped worrying.