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TBH after looking at the others they seemed less suitable. They seem to require custom trays for the bins and they are focussed on bigger commercial size bins. But seems to be plenty of options so I'm sure you can find something if it's acceptable as a solution.

Based on what they say, maybe it would be sufficient to provide storage space/charging connection for an electric assistance device to move the bins, without actually committing to purchase one?

Gah, well this got on my mind so I went down a rabbit hole. There's a whole range of solutions out there: https://www.mastermover.com/applications/bin-mover https://bintowa.com/ https://www.industar.co.uk/product/tow-tugs-electric-movers/small/ https://wheelieezy.com.au/ https://emoveit.com.au/product/wheelie-bin-aluminium-trailers-3-x-240l-bins All look pricey or need a car/buggy but if its the difference between using the plot or not maybe worth it as a last resort.

Where precision/accuracy/sharpness matters people want to use things that they are comfortable with.

I expect there is a much simpler solution to this but I've seen someone on youtube build little motorised trolleys for their bins to take them out front. If you get stuck on this then something to consider. Having said that the one I've seen was based on a guide track and simple motors. If you don't own the road and can't alter it then you'd need something more sophisticated (and the more sophisticated the more difficult I guess it would be to get approval). I'd guess all you need is for something to make it easier for a less able person to move the bin.

@SimonD Is this available online somewhere? I've found https://waterregsuk.co.uk but that doesn't seem to have the same content as the photo you posted.

sorry, was saying it in the context of multiple acceptable solutions as discussed above. Informed specifier has the leeway to allow the installers choice of options within an acceptable basket but say no to crap options.

So everything leading towards pipe in pipe sandwiched at the join between eps and pir (likely chased into eps). so you get: - pipes insulated by the eps pir sandwich - spaced to separate hot and cold - individually ducted for easy replacement if needed - minimal disturbance to the insulation. Ie cutting is way less than 50mm Though as @saveasteading is paying someone to do this maybe the biggest decider is what his installer is most comfortable with?

My only experience with low energy input is when my last boiler failed and I used the immersion. 3kw rated immersion seemed to have no trouble getting my 170L tank up to temp within an hour (from too cold to shower to plenty warm enough - can't be more precise than that).

Thanks for the update and I'm glad you are trying this. I assume with the controller still in the upper bedroom? If our guesses about your building are correct, it will take some time to warm. So while you are running this experiment I suggest the following: 1. Keep internal doors open - you want the air to be able to move around to equalise all the internal space* 2. Daily, open the windows for a good ten minutes to ensure the place has a good blow through (I think you said you did this anyway). 3. Regularly check the radiators with a thermometer ideally something like this: https://www.amazon.co.uk/ERICKHILL-Thermometer-Non-Contact-Adjustable-Emissivity/dp/B0C72MDQ2Z?crid=2V242L59HQZZ8&sprefix=ir%2Bthermom%2Caps%2C225&sr=8-6&th=1 The radiators should be warm and at approximately the same temperature (guessing around 50C) if the room with the thermostat in it is colder than 16C. If some radiators are colder than others or if the radiators are often not hot then there may be a problem with the system that needs fixing before things will warm up. *If you get hot at night or if you leave the bedroom window open at night, close the bedroom door to isolate the room from the rest of the house. You can also turn that specific radiator off at night and back on in the morning if it helps with bedroom temp (a good idea if you have the window open anyway). I know you said you will try this for 2 months but if you don't feel things improving at all in 2 weeks then maybe come back then.

My remaining thoughts are that I think I would want a duct, rather than direct bury. I'd want to be able to swap things out if there was a problem. If you are willing to put on top of the 150mm eps, then insulation not so needed. Could run individual pipes in conduit then so you could always pull/replace the pipes (like they do in many european countries). Much lower profile this way too.* I'm sure you've got another duct going in for electric stuff but I would try and put at least one more in for future needs. Probably won't use it but if a future need develops and you haven't got it then you are in a world of pain. * No expert so don't know if there is a flaw in this approach I'm not thinking of.

https://barkeepersfriend.com/

DHW definitely the limiting factor, depends how you design your system whether it's an issue. If the tank is big enough to handle the morning (or evening) routine in one hit with room to spare then reheat even if long shouldn't matter too much, just comes down to scheduling. If heat loss is 2.8kw, a 4kw unit can spend several hours a day on hot water (not all at once) and still have capacity to heat the house. Or have I missed something? This depends a lot on the heatpump though doesn't it? @JohnMo was talking about how his new 4kw heatpump had a much bigger external heat exchanger/radiator which should lead to a lot less icing/defrosting than his previous 6kw (downrated 9kw?) unit. Edit: I should add that Nick and Simon are the experts with experience, I'm not, just someone who is interested in this and trying to solidify my knowledge.

If these use the same internals then it's likely the minimum modulation is the same on both. If that's true then there is no benefit for going with the smaller model. Which means with a max heat loss of 2.8kw and a 7kw heatpump you will likely see a lot of cycling which is not great for efficiency. I feel like I'm channelling @JohnMo, surprised he hasn't spoken up yet.

Neither? Even 5kw sounds a bit big. Smaller heatpumps are available, Important to get one that can moderate it's output down a lot. Most of the year you'll need a lot less than 2.8kw