ReedRichards

I've never worked out why Octopus think "Octopus Cosy" is suitable for a heat pump. Presumably you think it is vaguely suitable, @Ronny?

No control by Water temperature in AI (Auto) mode gives you Weather Compensation. Control by Air + Water (temperatures) gives you Weather Compensation plus Load Compensation.

Surely you have some idea based on how much your GSHP was costing to run? Real data will always trump an evaluation.

For those not in the know, "AI" (Auto Mode) is what LG calls its Weather Compensation mode. Only later models of the LG Therma V will tell you what the outside temperature is, so I presume that is what you have. I'm hoping to get hold of a manual for the current range; when it comes I'll look in that and let you know if I find anything. In the short term, I would ask your installer to ask LG if anything can be done.

But I doubt that they evolved wearing clothes. Clothes are what should enable you to feel comfortable at lower temperatures.

I think the fundamental problem is that third party controllers switch mains voltage (AC) to control DHW. The LG heat pump uses both mains voltage (AC) and logic ( 5 V DC) to control hot water so it does not interface with a third party controller. A DIY solution to this issue is suggested by @ProDave on page 5 of this thread. I don't know if that's still working.

By the way, @Boy1925, LG should have received a broken 2020 vintage Therma V heat pump this week (my old one). If you are still waiting for spare parts, they should be able to cannibalise that to keep you going in the short term. My issue was a refrigerant leak, all the electronics should be working.

AFAIK the dongle I mentioned is only for monitoring and does not allow you to change settings. You can set the DHW temperature on the controller by using the L/R arrows to select the shower head icon then the up and down arrows to change the set temperature. Or you can go to Menu then Schedule then Schedules and Edit and schedule different hot water temperatures at different times. If you have a schedule already set this will override any manual changes as soon as the next scheduled timeslot starts.

The issue with an ASHP, I think, is that you will need a low power output to heat your house and, I think, a higher power output to heat your hot water in a reasonable amount of time. So you would need an ASHP with a good dynamic range of power inputs. Also, some ASHPs seem to start up on full or high power and then work their way down whilst others start at low power and work their way up. I think the latter type would be more appropriate to a low heat requirement. I might be wrong about this, my ASHP starts low. But I have seen data from another ASHP user indicating that theirs starts high. I'm sure others her could comment about this.

I like the room where I sleep to be a bit cooler at night. I suppose I could manage that using a smart TRV on the radiator in the bedroom whilst making the rest of the house really hot on cheap night-rate electricity. Did nobody following this type of strategy have any comfort issues?

I haven't done much with the new unit so far, except program it with my old Weather Compensation settings. The software version is 3.06.6a instead of 3.05.6 on my old version. It reports the outside temperature, which the old version didn't. And it says "anti-freezing" instead of "defrosting", which I don't like so much.

Maybe I am reading this wrong but I would have thought that the sooner you get your pipes inside the thermal envelope of the house the better. No matter how well insulated, those pipes will lose some heat and if they do this inside the thermal envelope then it's not wasted heat.

I have been incredibly fortunate! My installer, who I rate very highly, was able to convince LG that because of the expense of paying him to carry out a repair under warranty, which is very time consuming with a refrigerant leak, it was better to supply a new heat pump. So now I have the latest version of the Therma V with improved controls and I have to learn about all the new features. I still can't quite believe it.

Too hot for me, I would adjust the Weather Compensation settings.

If the boost is to be temporary, you might need Smart TRVs. Or you remember to turn up the TRVs when you want to boost the heat and turn them down afterwards. Even then, if there is a room thermostat somewhere controlling when the heat pump is on or off it might not be on at the right time. In my experience, a Smart TRV will override a room thermostat so you can be sure the heat pump will run when you need it to. But if it ends up only heating the two boosted rooms then it might cycle.

If you only oversize some of the radiators then those rooms will heat up most quickly and the room with the smallest radiator, as a fraction of the calculated size, will be the slowest to heat up. This may or may not work for you. You could also end up with a situation where most of your radiators have been throttled by TRVs and your heat pump is only working to supply heat to a few remaining ones. This might well cause your heat pump to cycle and if these cycles are short that is generally thought to be a bad thing. The same thing would happen with a conventional boiler. Really hard core heat pump users don't believe in any sort of thermostatic controls and just use Weather Compensation and radiator balancing to give you the inside temperature you require. If you go down that road then there is absolutely no point in oversizing radiators.

The proper MCS calcs should match the size of your radiators to the needs of your house and thus determine the required power output from your heat pump (with allowance for time off heating hot water instead of the house). The calculation will have been made at a particular Leaving Water Temperature and a particular outside temperature. If you oversize all your radiators by roughly the same percentage you would be able to use a lower LWT than the one assumed in the calculation, which would enable you to operate the heat pump more economically. If you would like to use all bigger rads, get the MCS survey to redo the calculation assuming a lower LWT.

Funny that this isn't a routine feature of heat pumps. It almost seems like they copied what gas boilers do without thinking it through. Either that or most other climates are dry enough that defrosting is much less of an issue.

I live trap my field mice; live if I get to them in time, that is. Apparently it's not legal to poison them. If I'm prompt enough and the mouse is still alive it gets relocated to several miles away in the countryside, where it ought to have taken winter quarters in the first place.

My mice, which are field mice overwintering in the loft, love to chew up pipe insulation but so far have not touched the foil-covered phenolic type which I have used predominantly.

Are you able to do this? My WC "curve" is constrained to be a straight line, whereas I think it probably needs a kink in it around 0 to allow for time spent defrosting.

I did not know what to make of the numerous parameters but I was able to create a log file and send it my installer who thinks the problem is indeed a refrigerant leak, not the best news. But he has it in hand and has always responded very positively. I am fortunate that he gave me a WiFi dongle that fits inside the heat pump and enables a tablet (actually, it's my wife's tablet) to talk to the heat pump. The tablet runs some software called LGMV to do this. I have not made much use of this hitherto, but it came in very handy today.

I've had to turn off the hot water because there isn't nearly enough power to heat it up. Now I'm left trying to heat radiators with a flow of 31 and a return of 29. It's become apparent that despite the lack of heat going into the water, I am using much more power than usual. I must have suffered a significant loss of efficiency. So possibly the lack of modulation is a secondary effect because some expected threshold is not reached. I have only radiators so there is nothing slow to warm up. There isn't a motorised valve that can go wrong, as far as I can see.

Already tried that, left it off for approximately 12 minutes, but it made no difference. Good suggestion, though.

I'm experiencing a problem with my 12 kW monoblock Therma V, installed December 2020. As of yesterday it has stopped modulating. As always, it starts up at the lowest level of power, drawing approximately 2.3 kW. Normally it will gradually step up the power input as necessary but as of yesterday it is stuck at 2.3 kW and never increases (or decreases) significantly. It will heat my water up to about 30 C, which at the moment is heating my house to about 19 C. If have set it to ask for a fixed water temperature of 50 C but that makes no difference. There is no error message nor any indication that it thinks something is wrong. Has any other Therma V owner experienced the same problem and know (or can guess) what the cause/fix might be?