sharpener

The Intatec valves upthread are supposed to open at +3C so might open much earlier than you think. OTOH after some years of doiing nothing they might be stuck and not open at all. Ethylene glycol (= car antifreeze) is inherently higly toxic but some cos e.g. Hydratech DTX use de-toxifying additives, whatever they are. Propylene glycol is inherently less toxic and is used in Fernox HP-5C and Alphi-11. I don't recall right now what the many others are based on, some product details near top of thread.

Think you might mean 120%(!) Not all of it especially as there is another 600kWh from the second array. Eventual plan is to get a smart meter before Radio Teleswitch turned off in Mar '25. Bc of poor coverage this may have to wait for wi-fi metering currently in development. And then move from deemed export to Octopus Outgoing. Even so it will only be a few £100s p.a., worth much less than my 2011 FITs which as you can see are a nice earner.

We have 6.9 kW on a due south facing roof in Devon, could hardly be better for insolation. But the generation in winter is only 1/10th of the summer peak, this is how it looked last year for the original 3.68 kW array. (The newer 3.24kW looks virtually identical, so the year's total was 7144 kWh which is 1032kWh per installed kW):

Not really an ASHP answer but is she on the latest kind (apixaban or edoxaban)? Feeling cold is not I think a common side-effect but thyroid problems are notorious, has she been checked for that?

That would put you at risk if there is a problem as you would have to pay Alto in full first. As per @saveasteading's post the normal route is the installer applies for the BUS voucher on yr behalf, then they claim the grant after commissioning. If there is a problem it is them at risk, you only pay them the net amount. From the OFGEM guide for Property Owners: 5.41. Once the property owner has provided consent and subject to all eligibility criteria being met, a voucher will be issued to the installer. The property owner will also be informed. Completing the project 5.42. Once a voucher for an ASHP or biomass boiler is issued,56 the installer has three months from the date the application is approved to complete the installation in line with industry standards and scheme requirements, and to register the installation with MCS and to redeem the voucher. Installers will have six months to do this for GSHPs.57 MCS may get in touch with the property owner regarding the quality of the installation.

Yes, rated more generously than many other mfrs. Hence I have been quoted for a 12kW Vaillant unit in place of a 15kW Stiebel Eltron. Full performance tables (in Czech) are here starting at p34. Extract for 5kW unit at 40 - 45C flow temp (modulation is better than I thought):

Depends quite a lot on your emitter setup. If you have (or fit) rads suitable for a 45C flow temp then from this table a 5kw Arotherm plus would do the job down to -2 OAT (southern England). Further north you would defo need the 7kW unit. With a SCoP of 3.77 your 18500 kWh would require 4907 kWh of electricity to generate, which is what you originally asked, multiplied as @SteamyTea says by maybe 70% to account for the (in)efficiency of the boiler. Depending on yr HW usage (which I assume is included in the 18500) you may also need to make a correction for the fact that producing HW will be at a lower CoP, I do not know if this is included in the SCoP formula. The 7kW unit has a higher SCoP so would use less, the downside would be more cycling in warmer weather, unlike a gas boiler they only modulate down to about 50% rated output, then they cycle.

When I extended the rainwater supply I put in 15mm polypipe mains water pipes to supply drinking water to the bathrooms. They go up into the loft and down again. I didn't consider the possibility of air locks at the time and there has never been a problem since.

Yes that is what I am proposing to do (and Vaillant have approved, with the filling loop and expansion vessel on the return as is their usual practice), but still with the zone valves shut and only one antifrost valve fitted à la @HughF there is no obvious way for air to get in so the water can get out of the external unit of the HP.

It's not the average you need to worry about. For example the mean February figure for Plymouth is +6.2C However to guarantee adequate HP performance the figure I need to use (from CIBSE Guide A) is -0.2C But for frost protection purposes the lowest temp in Plymouth in the last 10 years is -4.9C. And here on a tidal estuary just 20 miles away there was lying snow for a week in ?2009 and the river was iced over. Hence I would want to have protection down to -5C, and the Fernox HP-05 (or forthcoming Hydratech equivalent) seems well suited to this.

Some low tech solutions: A security camera will send you an email or pics every x hrs e.g. pics of your indoor/outdoor themometer. A burglar alarm - with its own battery backup - will phone or email you on break of a door circuit. This could be a relay contact held closed by the mains. Also if someone opens the cover of your HP. A Victron inverter will email you if the grid fails (or a number of other fault conditions). You can configure it so the battery always has a minimum SoC for this eventuality. I think you can also get Victron central to email you if it loses contact with your inverter. I am sure there are utility programs which would ping your router periodically and let you know if it is down. Do not rely on only one method. I worry about the migration of phone lines to VoIP, today's stats of 3.9M out of 35M smart meters not working properly does not fill me with confidence about national roll-out programmes.

No, the schematics for my proposed system (as approved and drawn up by Vaillant tech) re-use the existing n/c S-plan valves inc DHW to save the need to replace any of them with a diverter valve. So in a power cut all 4 circuits will be shut off. The only other flow path is an automatic bypass, but if the HP is not running there will be no differential pressure to open it. Thinking about some more, this is not a peculiarity of my system. The normal published Vaillant schematics have a HW diverter which defaults to the heating circuits, and then if these are more than one there are either zone valves or UFH actuators or both, all of which will shut off in a power cut.

So you are happy to rely on a single £30 Chinese copy valve to protect a £000s installation. I would not be confident that with only one valve it would allow enough air into the pipework to make sure all the water emptied out of the outdoor unit. Especially if the system is off and all the two-port valves are shut. Seems to me an ideal setup would isolate everything that is outside the house and then empty just that. To be independent of the mains it would need e.g. spring-loaded valves connected with bowden cables. Not easy to engineer to be reliable at reasonable cost though. Intatec valves in the video upthread look reasonably well thought out but as with all valves you cannot be sure they are not going to be stuck shut just when you need them to open. Then if they do you still have the hassle of re-filling the system before you can use it. And if it is < +3C how do you get the valves to stay shut for long enough to get the system running again, do you need an assistant to keep pouring hot water over them? For all these reasons I prefer to think in terms of glycol as per this thread.

Well at least the system will be well flushed. Don't see why you would now need glycol until September, why not just use inhibitor over the summer? Or 10% Fernox HP-5C at most, see link below. By co-incidence I watched this vid from Glyn Hudson yesterday, at 11'30" in he puts an elbow over the top of the AFV specifically to let the air get at it. [Edit - I see that is to break any vacuum, not to expose it to the OAT.] Also has only one valve, mostly I thought they were fitted in pairs, that's what Midsummer Wholesale supply by default. If you buy two it costs as much as a good load of glycol. Personally as I will need ~50 litres I am waiting for Hydratech to bring out their 5 deg protection product as per this thread.

Thanks for the heads up. But as you may recall my application is to stir the tank to improve the heat transfer with a small coil. There is 1.05m head at zero flow, and it will do 0.9m^3/hr at zero pressure which should be fine, I don't need it to turn the tank contents over every 20 mins, just keep it moving.

Thanks @mk1_man, I have been following your thread in Other Heating Systems (Mods, why are there two different boards covering ASHPs?). Presumably another advantage of going this route is you avoid paying VAT on a retrofit. But as I wrote there "Alto don't list Vaillant on their web site but I will enquire, don't want all the design work around their 12W Arotherm Plus to go to waste." Also AFAIUI the larger Mitsis are still R32.

Looks very interesting. Am returning to this theme as am getting frustrated with my potential installers, they applied successfully for the BUS voucher but now seem unable to install before it lapses. Alto don't list Vaillant on their web site but I will enquire, don't want all the design work around their 12W Arotherm Plus to go to waste. @markocosic posted a thread on LinkedIn here about design-only and MCS umbrella schemes. As that was last September it would be good if he could give us an update to the list here and let us know what he eventually did. Octopus' web site declines to quote at all for a house in the SW. Good Energy's web site have just re-quoted me £11200 net after BUS for 2 x 12 kW Midea, based on what data I have no idea, maybe looked up the EPC online. Last year it was just 1 x 16kW Midea for £6734 (after the then £5k grant) which was at least a better match for my calculated 12kW heat loss. Underwhelmed by their process though their tame EPC surveyor good value at £60.

Thanks, I will contact them tomorrow. Seem from their website to be a Mitsubishi specialist.

Sounds extremely competitive. I am in the S Hams, could you post their contact details here please @Surfiejim and @Tom, or PM me if you would rather.

Yes, connect output of flow switch to the coil of a substantial mains relay or small contactor. Connect normally open contacts of relay between mains and the pump. I still think the original fault is very odd as there appears to be some 20V across the reed switch contacts, this implies current is flowing but the contacts are high resistance so power is being dissipated. I would expect either 240V if they are burnt away or virtually nothing if they are making. Did you measure the voltage directly across the contacts?

I would expect them to be industry standard bearings and you can probably get them from simplybearings.co.uk, they may even know what it is you need. I fitted their SKF bearings to the AEG motor in my oil boiler. It was quite easy to dismantle and obvious how to fit the replacements, just needed a wooden drift of about the right size, it has been running OK for two seasons since I did it. So that would be the way to go IMO once you don't need the heating for the summer.

There's no consistency to this. My proposed HP is too big for PD, but the LPA have granted permission without any reference at all to noise standards, MCS or otherwise. Still open to challenge but that would have to be under the legislatation about nuisance, not any aspect of planning law.

Unless you have substantial insultation in the ceiling/first floor you will find a lot of heat makes its way up to the first floor whether you "heat" it or not.

That's for the central heating circuit. Why do you need to drain that? It looks as though the cold feed and hot outlet are on the rhs of the tank but I can't see the actual valves, only the pressure relief arrangements. Needs better picture without all the junk in shot. Also answer the questions @ProDave poses upthread.

Ambitious if they think it can be fitted in a day. Sounds well over-sized for a 150m2 new build. Have used Heatpunk, good agreement with my installer's heat loss survey. There are a few bugs, mainly to do with calling up correct rad types - which won't bother you. Cross check the result here, it suggests you are in the 3 - 6 kW range, not 12! Unfortunately we are over a barrel bc Vaillant will only provide extended warranty if fitted by their approved installers.