wierd overnight power draw of LG Therma V R32 monobloc 9kW AWHP

[chris47]

Hi All

 

Compare the 3 attached photos of my give energy & shelley apps; it shows these odd early morning power draws of my LG AWHP.  The give energy photo dated 7/9/25 is what I expect & have seen over the last few months; the give energy photo dated 11/9/25 shows these weird spikes occurring every hour or so; the shelley photo shows overnight AWHP consumption of around 500Wh every hour throughout the night whci seems to tally with the give energy graph of 11/9/25

I've checked the CH schedule on the Honeywell Home room thermostat as follows:

P1 starts at 05:00  - CH ON
P2 ends at 16:00  - CH OFF
P3 starts at 19:00  - CH ON
P4 ends at 23:50  - CH OFF

 

HW schedule:

06:00 to 07:00
13:00 to 16:00
22:00 to 00:00

The lowest temp last night (11/9/25) was 12°C between 03:00 & 06:00; any ideas about why this AWHP behaving like this would be appreciated.

[JohnMo]

May depend on what your thermostats are set too. Maybe the house has started to cool more over night than it did, and is now hitting your set back temperature, so heat pump is blipping heat in to keep things happy.

 

Aren't you running weather compensation?

[ProDave]

Do you have individual metering on the ASHP if so which ctace is that on your graph.

 

My 5kW LG therma V does indeed turn on it's circulating pump as it sees fit if the water temperature drops below 10 degrees and circulates for a few minutes.  the colder it gets the longer it needs to circulate to warm the water by stealing some heat from the house.

 

It is presumably a frost protection routine that is not mentioned anywhere in the manual, does not appear anywhere in the setup and cannot be turned off.

 

But it is only the circulating pump in my case.  However I have all use of the internal willis heater turned off.  I seem to recall if you have enabled the internal heater functions, that it may turn that on as part of it's frost protection routine.

 

It is a shame this function is not properly documented.

[JamesPa]

Have you got a buffer between ashp and emitters?  If so then, depending on how your installer has set the controls up, it could be turning on to heat the buffer up when it gets cold outside, even if there is no call for heat from the rest of the system.  

Edited 14 hours ago by JamesPa

[chris47]

2 hours ago, ProDave said:

Do you have individual metering on the ASHP if so which ctace is that on your graph.

 

My 5kW LG therma V does indeed turn on it's circulating pump as it sees fit if the water temperature drops below 10 degrees and circulates for a few minutes.  the colder it gets the longer it needs to circulate to warm the water by stealing some heat from the house.

 

It is presumably a frost protection routine that is not mentioned anywhere in the manual, does not appear anywhere in the setup and cannot be turned off.

 

But it is only the circulating pump in my case.  However I have all use of the internal willis heater turned off.  I seem to recall if you have enabled the internal heater functions, that it may turn that on as part of it's frost protection routine.

 

It is a shame this function is not properly documented.

Thanks for your comments ProDave

 

The Shelly EM GEN3 monitors the AWHP (LG Therma V AWHP on right hand side of Shelley app).

The power draws are 1.5-2kW approx, far larger than a circulating pump would draw.

There is an adjustable frost protection routine but it's not well documented but whatever I set it to doesn't appear to make any difference to the timing of the power draw.

There is no immersion boost heater installed in the buffer tank as installers state they don't fit them in UK installations because our climate is not cold enough.

The LG installation manual is not well written but my thinking is that there is a low power immersion heater (IH) fitted inside the LG AWHP monobloc cabinet. This IH is switching on, at approx hourly intervals, as a frost protection measure.

The legonella IH is fitted but have switched it off, so the power draw is not due to this.

On the give energy graph dated 11/9/25, the power draws between 00:00 & 02:30 are typical of an inverted (modulating) AWHP compressor draw. Between 02:30 & 04:40 the power draws are more like an IH.

 

I wonder if it's worth contacting LG support?

[JamesPa]

Just now, chris47 said:

There is an adjustable frost protection routine but it's not well documented but whatever I set it to doesn't appear to make any difference to the timing of the power draw.

So you have a buffer tank?  The heat pump may be switching on to heat it up even though there is no call for heat from the secondary side, depending on how your installer has set up the control system.  Has this started only when it got colder at night outside and is this your first winter?

[chris47]

9 minutes ago, JamesPa said:

Have you got a buffer between ashp and emitters?  If so then, depending on how your installer has set the controls up, it could be turning on to heat the buffer up when it gets cold outside, even if there is no call for heat from the rest of the system.  

Thanks for your comments JamesPa

 

There is a a buffer tank between AWHP and emitters, built into the base of the HW tank but no IH is installed there

[JamesPa]

3 minutes ago, chris47 said:

There is no immersion boost heater installed in the buffer tank as installers state they don't fit them in UK installations because our climate is not cold enough.

So you have a buffer tank?  The heat pump may be switching on to heat it up even though there is no call for heat from the secondary side, depending on how your installer has set up the control system.  Has this started only when it got colder at night outside and is this your first winter?

 

The fact there is no immersion is irrelevant, its the heat pump which will switch on if the system is wired in the way it might be

Edited 14 hours ago by JamesPa

[chris47]

3 hours ago, JohnMo said:

May depend on what your thermostats are set too. Maybe the house has started to cool more over night than it did, and is now hitting your set back temperature, so heat pump is blipping heat in to keep things happy.

 

Aren't you running weather compensation?

Thanks for your comments JohnMo

 

My house is well insulated (EPC high C rating) so heat loss is low; however, the thermostat schedule is OFF until 05:00 but the power draw is much earlier.

My AWHP was only installed in April 2025 so my installer stated there is no historical data yet. He will setup weather compensation after 1 year's running.

[chris47]

8 minutes ago, JamesPa said:

So you have a buffer tank?  The heat pump may be switching on to heat it up even though there is no call for heat from the secondary side, depending on how your installer has set up the control system.  Has this started only when it got colder at night outside and is this your first winter?

There is a a buffer tank between AWHP and emitters, built into the base of the HW tank but no IH is installed there. Yes, this is my first winter

[ProDave]

8 minutes ago, chris47 said:

There is an adjustable frost protection routine but it's not well documented but whatever I set it to doesn't appear to make any difference to the timing of the power draw.

I have never found ANY documentation on that, so can you share what you know please?

 

9 minutes ago, chris47 said:

The LG installation manual is not well written but my thinking is that there is a low power immersion heater (IH) fitted inside the LG AWHP monobloc cabinet. This IH is switching on, at approx hourly intervals, as a frost protection measure.

The IH I referred to is what is generally known as a willis heater, a standard immersion heater in a tube with a low volume of water passing through it.  There is definitely one in mine.  The LG manual referrs to it as a stage 2 heater, used for example if you want very hot water for instance.  I have disabled all forms of stage 2 electric heating so mine never uses that now.  How practical are you?  you could always open the unit up and physically disconnect it?  My suspicion is if you have the stage 2 electric heating enabled, it might turn that on for it's frost protection when mine only turns on the circulating pump and steals some heat from the house.

 

Another theory is some heat pumps have a sump heater to heat the compressor oil.  I have not heard of that on an LG but of fitted can be a cause of unexpected use at idle.

[JamesPa]

14 minutes ago, chris47 said:

There is a a buffer tank between AWHP and emitters, built into the base of the HW tank but no IH is installed there. Yes, this is my first winter

OK.  A possible explanation is this:

 

Installer has kept the control systems on the secondary (emitter) side of the buffer totally separate from the control system (ie the heat pump controller) on the primary side.  Most of the time this works more or less as expected.

 

However when there is no call for heat from the secondary for a long time the heat pump has no way of knowing that.  So if its also cold outside, it tries to keep the buffer at whatever temperature it is required to according to the WC curve and other settings.  Thus it switches on occasionally during the night, draws power for a while, switches off because the buffer is warm and no heat is being drawn from it by the secondary.  It only switches on again when the buffer cools due to heat loss.

 

Stupid way to wire a control system IMHO if that is what has been done, but then putting a buffer in was quite possiblystupid also!

 

Was the honeywell etc already present when the installer fitted the ASHP.  If so he probably was trying to avoid touching it.

 

Feel the buffer tank (or better the pipes leading to the buffer tank) after this has happened, if its warm then thats the culprit, if its not warm then its something else.

 

 

 

Edited 13 hours ago by JamesPa

[ProDave]

We know ours is doing this frost prevention thing because we can hear the faint hum of the circulating pump come on.  Can you hear anything at all when it happens?

[JamesPa]

32 minutes ago, ProDave said:

We know ours is doing this frost prevention thing because we can hear the faint hum of the circulating pump come on.  Can you hear anything at all when it happens?

Frost prevention already?  I guess you are quite a bit further north than me! 

 

Its a good point though, I dont think we know where OP is, if he is in the south its not frost prevention, if quite a lot further North it could be.

Edited 13 hours ago by JamesPa

[ProDave]

44 minutes ago, JamesPa said:

Frost prevention already?  I guess you are quite a bit further north than me! 

Only done it once this autumn.  It has been down as low as 6 degrees overnight already.

[chris47]

20 minutes ago, ProDave said:

Only done it once this autumn.  It has been down as low as 6 degrees overnight already.

 

20 minutes ago, ProDave said:

Only done it once this autumn.  It has been down as low as 6 degrees overnight already.

 

1 hour ago, JamesPa said:

Frost prevention already?  I guess you are quite a bit further north than me! 

 

Its a good point though, I dont think we know where OP is, if he is in the south its not frost prevention, if quite a lot further North it could be.

I'm in Bristol (South West)

[chris47]

22 minutes ago, ProDave said:

Only done it once this autumn.  It has been down as low as 6 degrees overnight already.

 

22 minutes ago, ProDave said:

Only done it once this autumn.  It has been down as low as 6 degrees overnight already.

 

1 hour ago, ProDave said:

We know ours is doing this frost prevention thing because we can hear the faint hum of the circulating pump come on.  Can you hear anything at all when it happens?

 

1 hour ago, ProDave said:

We know ours is doing this frost prevention thing because we can hear the faint hum of the circulating pump come on.  Can you hear anything at all when it happens?

Not without staying up all night:) I'll give it a try tonight

[chris47]

1 hour ago, ProDave said:

I have never found ANY documentation on that, so can you share what you know please?

 

The IH I referred to is what is generally known as a willis heater, a standard immersion heater in a tube with a low volume of water passing through it.  There is definitely one in mine.  The LG manual referrs to it as a stage 2 heater, used for example if you want very hot water for instance.  I have disabled all forms of stage 2 electric heating so mine never uses that now.  How practical are you?  you could always open the unit up and physically disconnect it?  My suspicion is if you have the stage 2 electric heating enabled, it might turn that on for it's frost protection when mine only turns on the circulating pump and steals some heat from the house.

 

Another theory is some heat pumps have a sump heater to heat the compressor oil.  I have not heard of that on an LG but of fitted can be a cause of unexpected use at idle.

Can't it be disconnected via LG control panel on HW tank?

[JohnMo]

There are a couple of intermittent heating modes to protect the heat pump, the anti frost one - circulation pump on at or around a sensed 5 degs. The other is to keep the lube oil above dew point and a crankcase heater will fire up  but is generally 30 to 40W.  Neither really explain the the spike you see.

 

As @JamesPa says the ASHP may be firing to keep the buffer happy.  If the circulation pump runs all the time (some do by default) and it's cool outside the the temperature of the buffer will over an hour or so will drop, possibly enough for the heat pump to fire up.  Why with no demand for heat? A buffer cuts the heating system in half and both are hydraulically separate.  Your thermostats depending on wiring may only affect the CH side and not the ASHP side.  So your timer may only be stopping the CH circulation pump.

 

2 hours ago, chris47 said:

He will setup weather compensation after 1 year's running

That is just a poor excuse for sloppiness, there is no reason not to set up now.  He knows the design temp of the emitters, so first attempt should be pretty close.  By running a schedule you are running a higher than required flow temp - so a hit on CoP, the buffer is another hit on CoP, fixed flow temp another. 

[Dillsue]

13 minutes ago, JohnMo said:

That is just a poor excuse for sloppiness, there is no reason not to set up now.  He knows the design temp of the emitters, so first attempt should be pretty close.  By running a schedule you are running a higher than required flow temp - so a hit on CoP, the buffer is another hit on CoP, fixed flow temp another. 

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

[JamesPa]

2 hours ago, chris47 said:

I'm in Bristol (South West

So unlikely to be frost prevention then (I presume it's not getting down to 5C in Bristol yet)

 

This increases the probability that the heat pump is doing what it has been asked to do, and the 'problem' is due to a complete separation between the control systems either side of the buffer tank, as set up by your installer.

 

In a sense you shouldn't worry too much about it, the heat delivered will stave off the point at which your heating is properly on.  On the other hand it suggests, as @JohnMo says, a sloppy installer.  

 

You probably will benefit from some tweaks to your system which people here can advise on if you are willing to stay the course.

 

Edited 10 hours ago by JamesPa

[dpmiller]

have I missed any reference the DHW in this?

[chris47]

1 hour ago, dpmiller said:

have I missed any reference the DHW in this?

HW schedule:

06:00 to 07:00
13:00 to 16:00
22:00 to 00:00

 

As can be seen above, the overnight power draws are when DHW demand is OFF

[chris47]

7 hours ago, ProDave said:

I have never found ANY documentation on that, so can you share what you know please?

 

The IH I referred to is what is generally known as a willis heater, a standard immersion heater in a tube with a low volume of water passing through it.  There is definitely one in mine.  The LG manual referrs to it as a stage 2 heater, used for example if you want very hot water for instance.  I have disabled all forms of stage 2 electric heating so mine never uses that now.  How practical are you?  you could always open the unit up and physically disconnect it?  My suspicion is if you have the stage 2 electric heating enabled, it might turn that on for it's frost protection when mine only turns on the circulating pump and steals some heat from the house.

 

Another theory is some heat pumps have a sump heater to heat the compressor oil.  I have not heard of that on an LG but of fitted can be a cause of unexpected use at idle.

 

6 hours ago, JamesPa said:

OK.  A possible explanation is this:

 

Installer has kept the control systems on the secondary (emitter) side of the buffer totally separate from the control system (ie the heat pump controller) on the primary side.  Most of the time this works more or less as expected.

 

However when there is no call for heat from the secondary for a long time the heat pump has no way of knowing that.  So if its also cold outside, it tries to keep the buffer at whatever temperature it is required to according to the WC curve and other settings.  Thus it switches on occasionally during the night, draws power for a while, switches off because the buffer is warm and no heat is being drawn from it by the secondary.  It only switches on again when the buffer cools due to heat loss.

 

Stupid way to wire a control system IMHO if that is what has been done, but then putting a buffer in was quite possiblystupid also!

 

Was the honeywell etc already present when the installer fitted the ASHP.  If so he probably was trying to avoid touching it.

 

Feel the buffer tank (or better the pipes leading to the buffer tank) after this has happened, if its warm then thats the culprit, if its not warm then its something else.

 

 

 

The Honeywell wireless thermostat was part of the AWHP installation

[chris47]

5 hours ago, chris47 said:

Can't it be disconnected via LG control panel on HW tank?

I'll try to find the route to controlllng the frost stat temp settings I discovered by accident.