Dillsue

If and when you build the second house put in a meter box and ducting to your consumer unit for a future grid connection. If you decide to sell in the future, spending a few grand on a grid connection for the next owner will likely be more than recouped in the sale price versus an off grid setup. Piggy back off the existing house in the meantime if that works for you. If you put PV on the new house any surplus will go to the grid via the existing house connection. Remember that any DNO limits for the existing house will apply to the combined output from both houses! Make sure the cable between the 2 houses is big enough to carry the max any PV could generate without causing to much of a voltage rise.

According to the Therma V manual, 3rd party boiler, immersion and inline backup heater are all separate features with separate wiring and settings. The settings for the 3rd party boiler only offer an OAT trip point and a hyteresis value so the HP doesnt restart until its warmed up a bit. Won't be testing til the winter so will see how accurate the manual is then!!

The missing insulation is on the pipes within the HP omitted by LG, presumably because they expect the HP to run continuously, even though they have a feature to enable a backup boiler in cold weather. With all the bends, strainers, sensors and other pipework it would be difficult to get it all effectively insulated The trace heating manufacturer gave a table of insulation thicknesses needed for a particular size of pipe giving 25mm of insulation for 28mm pipe so that's what we've got. A genny powers it in anything but a short power cut. Having the trace heating is more for if we shut the HP down in very cold weather to run on the WBS rather than flog the HP. It will also protect it if it fails in cold weather and can't get fixed quickly. At £48 it's probably cheaper than antifreeze valves or glycol??

An alternative to glycol or antifreeze valves is trace heating. A £50/4metre length runs through our insulation around the outdoor pipes with a loop coiled up in the bottom of the HP under the water pipework. Our HP isn't particularly well insulated and most of the water pipework wasnt insulated at all. Ive added some insulation but there's still plenty exposed so hopefully the trace heating will keep any freezing at bay

The original part of the house had 8mm copper drops from ceiling to floor on 5 rads and I couldn't get any flow to 3 of them without shutting down the lockshield on the rest of the house. A small pump on the 22mm pipe feeding them has sorted that. Still got another rad with a long 10mm run to get flowing but Im confident Ill get that with balancing. Everything is plumbed direct so no separation

Balancing and WC setup can be done now. I wouldn't wait til winter to set things up in case you hit problems.....I couldn't balance the whole house and have had to shut the heating down to add a pump and control for it. Potentially could have been without heat for a couple of days which isn't a problem now but would have been in the winter

That's my understanding of how things can be configured. I'm in the throws of setting ours up and currently have it configured to run and stop on a volt free contact which is the same as an on/off stat. Once all the hydraulics are sorted I'll be moving onto WC(AI in LGs world) with the volt free contact acting as a temperature limiter or to disable the HP for other reasons. I could leave the volt free contact/stat disabled with a dip switch and the HP would just pump water as required by WC/AI

Isnt the default set up to use the room temp sensor built into the remote controller?? An external/3rd party thermostat, if fitted, has to be enabled with a DIP switch

If your trip voltage is configurable get them to raise it a couple of volts so you don't keep shutting down. Theres a pretty good chance that the voltage rise is just within your property and if you measured it at the point your cable connects to the grid it would be within tolerance. You can check by measuring the voltage at your neighbours incoming connection when you're exporting on a sunny day, assuming they'll let you! Get them to turn off any big loads when you measure the voltage.

If all your scheduling is done within the Honeywell programmer can you turn that off overnight and see if the HP continues starting up? That will rule out the programmer. If you think it could be the HP topping up the buffer then can you turn the buffer set point temp right down before you go to bed? That should stop the buffer being topped up.

I dont know what series Therma V the OP has but on our series 3 from 2020 the user can bias the WC curve from the indoor display. Should be straight forward to set it up and explain to any user when to tweak things

Let your DNO know and they'll have to do sort it out to keep within the 253v limit

60 ebay results on a search for "heat pump cylinder". Start searching and collecting well in advance of starting a project and most things come up at the right price:)

You could ask Mixergy if they considered or tested that set up? When they went down the PHE route it would have been fairly easy to test things with the PHE outlet feeding in nearer the top. In terms of manufacture its only going to cost a few extra £ to run the outlet up the side of the cylinder to the top, if it gave a performance advantage.

More than happy for your input. You're wanting to do fundamentally the same as me so interesting to hear your take on things. If your morning heating regime is based on cheap overnight eleccy remember that off peak tariffs are not always guaranteed be available....build in flexibility if you can

I'm sure they have more knowledge and experience than me

Our cylinder is 2 metres tall with a mass of pipework above and around the top so access isn't the best. Nearer the base is largely clear so less buggering about to put the return where I beleive/hope it will perform better. The flanges aren't cheap but not needing a 2 port valve for top return will pretty much offset the cost of the flange

?? If you don't want mixing at the top wouldn't you put the flange lower down? Mixergy have their return point around a quarter of the way up so I'm following their lead.......they've likely done extensive testing so I'm trusting that their positioning is optimal??

ASHP pumps through the PHE primary side in the same way it would pump through a coil in the cylinder. On the secondary side a potable water pump will draw cool water from the bottom of the cylinder via the cold water inlet. The pump will pump this water through the secondary side of the PHE. Heated water leaving the PHE secondary will be injected back into the cylinder via the Essex flange fitted part way up the cylinder. I'm aiming to fit the Essex flange about a quarter of the way up the cylinder to avoid the coils inside the cylinder and any seams

75mm of spray foam. Looks a bit of a stretch for gland pliers/pipe wrench so will need to find a box spanner or deep socket to tighten up the back nut

I watched Rogers video earlier and it does look straight forward and not as uncommon as I thought it was. I think Roger mentions a max temp of 60 deg C which is too low for us as the solar thermal can take the cylinder well above that. I had a look on the manufacturers web site and it says up to 90 deg C so a bit of investigation needed. Thanks for all the ideas and comments so far

I'm slowly coming round to the challenge just to get the HW entering in a better place. It's only 5 mins with a holesaw..........what could possibly go wrong:)

Be nice to be able to add a dedicated new tapping but the jury's out on that just now

Waiting to hear back from the cylinder manufacturer on viability of doing this. I'm sure it'll be a negative response but interested to know how they would add one in the factory..... I think they are soldered which is a bit of a none starter with spray foam insulation

Exactly. When we added more PV our DNO stumped up for a new transformer, 3 new poles, 100metres cable, pole anchors, earth loops etc. That brought the supply up to modern standards. The neighbours now run through the summer days on our PV. It's also meant that when we recently applied to hook up an EV charger and heat pump the supply was up to spec and got approved in a couple of days. I would imagine that much if not all of the cost of upgrades to hit net zero are coming from the bill payer and central government so minimal cost to the DNOs??