ReedRichards

I also have an LG Therma V and I had the same problem the first time I used the AI mode. However I tried AI again a few months later and the problem has not happened again since. Either it's a (lack of) learning thing by the LG controller and/or the room thermostat. Or you have the temperatures for auto mode set incorrectly. With the parameters you are using if the outside temperature is +3 C then the maximum leaving water temperature will be 45 C. Perhaps that's not enough? If it happens again I suggest you switch from AI mode to direct temperature control and set the Leaving Water Temperature to 50 C. If that does not work then there is really something wrong.

I'm not aware of any general purpose thermostat that is particularly well-suited to control a heat pump. But you may be able to tell your thermostat that it is controlling an oil boiler which should prevent it from trying to run very short cycles.

It seems to me that if you mix radiators and underfloor heating then whilst the radiators are on you need the leaving water temperature from your heat pump to be high enough to suit the radiators so you don't get the efficiency/CoP benefit that you would from a house that uses just UFHs and so can use a lower leaving water temperature. Possibly if you have the UFH on all of the time and the radiators on some of the time then the heat pump can be programmed to reduce its leaving water temperature when there is no demand from the radiator zone. But I'm not sure if the control for my heat pumps is sophisticated enough to do that.

There is still Economy 7, a very basic time-of-use tariff.

Logically you should charge (heat-up) your hot water tank when the outside temperature is warmest so around noon should be a good time. The hotter you keep your tank temperature then the more heat will be lost to the surroundings, although in winter that may not be a terrible thing because the heat will be lost to the house. The cooler you keep your tank temperature the more efficiently your heat pump can heat it but the more chance there is that the hot water will run tepid. In my case my hot water is set to 50 C and it is on from 6:30 to 22:30 so it just recharges as necessary. However the hysteresis setting is set to 10 C so it should not recharge until the tank temperature drops to 40 C or less.

Ah, so that's it; 45 C would be much better suited to a heat pump. Do you have to pay a premium for a non-standard PCM? I agree, although if you don't have an airing cupboard then the compact size might be particularly useful.

A heat battery uses a phase change material that can absorb and re-transmit a lot of heat at one particular temperature, the temperature at which the phase change takes place. The standard Sunamp heat battery uses a material where the phase change takes place at about 58 C. So to charge a Sunamp heat battery with water you need to supply it with water at above 58 C (it could be just above) and the water leaving the battery will be at 58 C. It's pushing a heat pump to achieve that sort of water temperature and if it can do it then the CoP will not be good. On the other hand if you are heating a tank of water then every degree by which you raise the temperature takes the same amount of energy so if you are heating from cold you start off with a good CoP which diminishes as the tank temperature increases. In my case the tank temperature is set to 50 C and the leaving water temperature gets to about 55 C to achieve this. So you have the option of a heat battery where almost the entire charging process takes place at a temperature where the CoP will be poor or a tank of water where only the last few degrees of charging will approach a similar poor CoP. Therefore I was surprised to read that some contributors use heat batteries because I would have thought they were ill-suited to efficient use with a heat pump. Am I wrong?

Your MCS-accredited installer needs to sign-off on the installation before you can make an RHI claim. They are the person who can answer your question authoritatively.

Traditional radiators mostly work by convection rather than radiation. They heat the air which rises out of the radiator and draws in more cold air from below. You can increase the efficiency of heat transfer by blowing air through the radiator so a fan-assisted radiator can be smaller than a "traditional" radiator and achieve the same heat output (for any given water temperature). If that's what "work better" means then it's true. But if your guy is implying that the lookup-tables you use to calculate heat output from a radiator at lower temperatures are wrong and overestimate the heat output then that is news to me.

I'm fully aware that it's not an issue for me. I'm just curious if anybody at all has a meter on their immersion heater. Or is it a requirement that simply isn't adhered to?

Perhaps I did not make myself clear? My ASHP was installed a year ago. I did use the RHI. Therefore I do have a meter measuring the electricity drawn by my heat pump (because it's now a requirement of the RHI even though I can ignore the readings if I wish). But the immersion heater in my DHW cylinder has its own circuit and is not metered. Then I read: When my heat pump was first installed it had full control of the immersion heater and I had to get that rewired so I could also control the immersion heater independently (if the heat pump was not working, for example). But it looks as if had I not done that then my installed omitted to put a meter on the immersion heater circuit. Or am I wrong?

I've just been reading the "Essential Guide to Metering" (May 2018 version) and this mentions metering the immersion heater. My immersion heater can be controlled by the heat pump or controlled independently. Under these circumstances it looks as if I don't need to meter the immersion heater. I don't have an immersion heater meter but the independent control capability was a retrofit modification so maybe I should have had. What is the norm for recent installations that require metering of the heat pump?

Running an ASHP in cooling mode would prevent you claiming RHI or getting a waiver on Planning Permission.

1) A tank only takes up the space of a floor-to-ceiling cupboard and if you put it in the loft then any heat lost from the tank will be not be wasted when you convert the loft. 2) You will not run out of water if you size the tank correctly. 3) You really use no hot water apart from for showering? What is also very inefficient is to heat your water using direct electrical heating when you can heat it for 1/2.5 (ish) of the electricity and cost using a heat pump. 4) You are likely to need a buffer tank for your central heating. Often this is placed below the hot water tank as a single unit.

This struck me as odd. You have the option to set the Temperature Sensor to be Air or Water or Air + Water. If you have a Hive room thermostat then selecting Air or Air + Water would surely cause the Hive to "fight" the LG controller as they are both trying to set/control an air (i.e. room) temperature. So, I think, the only sensible option is to select Water (being the leaving water temperature) as the parameter used for control. If so then the Indoor temp for auto mode is irrelevant (or N/A as it says in my installation instructions). You can set whatever values you like but it should not make any difference.

I have only just found this thread but see here: for how the Auto/AI mode works. In my case (all radiators) the settings (as recommended to the installer) are: Outdoor Temp for Auto Mode: Min 5 Max 19 LWT for Auto Mode: Min 34 Max 50 So if the outdoor temperature is 5 C or less then the Auto mode does not operate and the leaving water temperature target will be 50 C. By the way, my system has two pumps, one inside the Therma V and another for the central heating inside the airing cupboard. The latter is not at its maximum output speed. I had to tell my central heating controller that my heat pump was a oil boiler in order to prevent it from short-cycling.

Some Youtube videos have been made giving an installer setting guide: Monobloc: Split:

I'm on software version 3.05.6a. is that the latest one?

Soon after my ASHP was installed it went wrong with the CH14 error (it was a blocked filter). To my frustration, I found that in this error state I could not operate anything, including the immersion heater. I now have a switch for my immersion heater wired in parallel to the LG control box so I can operate the immersion heater under all circumstances. Without such parallel wiring you may well find that if something goes wrong with the heating you don't have the option to heat DHW via heater.

Many people have a hot water cylinder in their airing cupboard. This too is a thermal battery. The advantage of thermal batteries like the Sunamp are that they are more compact, for a given amount of stored heat, than a tank of hot water. The disadvantage, last time I looked, is that they are more expensive.

Further to my previous post I have checked and I don't have the option to schedule the DHW Heater. This must be because my setting is "Use Disinfect".

By "DHW heater" I presume you are using the LG terminology and mean the immersion heater inside the hot water cylinder? You probably want to use that as little as possible as it is much more expensive than heating your hot water via the heat pump. There is a three option setting for this immersion heater "Use / Use Disinfect / Not use". I have mine set to Use Disinfect so I can heat the water in the cylinder to 60 C once a week as a precaution against Legionella. Therefore I don't try to schedule use of the immersion heater and I don't think I have access to the Boost function. To answer a question with a question, why do you want to schedule use of your expensive immersion heater? You've bought a heat pump, why not save money and just use that to heat your hot water? You can read some data towards the bottom of the list of installer settings.

Anybody read Dutch? There is quite an active group of LG Therma V users here .

Your minimum outdoor temperature is much lower than mine. As a consequence your Leaving Water Temperature will almost never (if ever) reach 46 C; only when the outside temperature is -7 C or less. With your settings' the LWT will be 43 C when it is 0 C outside, 40 C when it is +7 C outside and 37 C when it is 14 C outside. Then add-in whatever number your AI is set to.

This is what I was guided by: