Dillsue

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