LG Therma V mono block Air Source Heat Pump

[ReedRichards]

Yes, I did mean the immersion heater for the hot water.  My buffer tank also has an immersion heater but it's not wired in, so it's there but not used.

[ProDave]

As far as I know there is no way to manually turn on the internal willis heater.  It uses it under certain circumstances to legionairs cycle, for defrosting, and as an emergency heater under some fault conditions.

[ReedRichards]

@ProDaveSurely the heater you refer to is part of a closed loop and does not need to legionella cycle?

[ProDave]

19 minutes ago, ReedRichards said:

@ProDaveSurely the heater you refer to is part of a closed loop and does not need to legionella cycle?

I am talking of the Willis heater, inside the heat pump, in line with the heat exchanger.

 

As far as I can tell it has 3 uses:

 

DHW heating it is used in the final stage of DHW heating to get the temperature higher.  The default settings on my unit always used this.  I changed the settings to only heat my DHW to 48 degrees with a maximum flow temerature of 55 degrees and not to use the willis heater.

 

It is used when the heat pump goes into defrost mode to reduce the amount of heat it has to suck out of the hot water tank.

 

It is used as an emergency heater if some part of the heat pump fails.

 

The only one of those you have any control of is the DHW heating cycle.

 

I don't know if the willis heater is used as well as the immersion heater in the hot water tank for the legionairs cycle as I have that turned off.

[ReedRichards]

On the outside of my hot water cylinder is a large box (see picture).  I don't know if everybody gets one of these but it's function is to allow the LG controller to turn on the immersion heater (that is just below it) which heats (or can heat) the DHW.  AFAIK this is used solely to raise the temperature of the water to 60 C for the legionella cycle.  To use the Willis heater as well would be belt and braces, surely?  And if you could use just the Willis heater then that big box would be redundant.

 

What you can't quite see in the picture is that I have two wires going to my immersion heater.  They are both on the same circuit but one goes via the box and one goes via a switch that I can operate independently.  I just wondered if that was the norm.  I had to do a bit of persuasion to get it done that way and I was chatting to someone who "lost" their immersion heater switch when their new cylinder was installed.  

[ProDave]

Yes that's the standard immersion control box, it contains a contactor and a circuit breaker.

 

I don't like your idea of a parallel connection to the immersion heater.  Okay IF the person wired it knew exactly what they were doing and it comes from the SAME circuit.

 

What I did was put a switch next to the box that manually energises the contactor in the box, so the immersion heater gets turned on in the same way should you want to use it manually.

 

And further, I added a solid state relay, part of my home made solar PV dump controller, to the box so the SSR bypasses the contactor as well to feed surplus solar PV power to the immersion heater.

 

[SteamyTea]

3 hours ago, ProDave said:

is used when the heat pump goes into defrost mode to reduce the amount of heat it has to suck out of the hot water tank.

Why would you do, or want, that to happen.

CoP of 1, compared to over 1.

[ProDave]

9 minutes ago, SteamyTea said:

Why would you do, or want, that to happen.

CoP of 1, compared to over 1.

I did not program it.  I just observed what happens, when it goes to defrost it turns on the willis heater.  It does result in a very quick defrost cycle. 

[dpmiller]

it must presume there's no buffer volume then?

[ReedRichards]

On 06/04/2021 at 09:43, ProDave said:

Yes that's the standard immersion control box, it contains a contactor and a circuit breaker.

 

I don't like your idea of a parallel connection to the immersion heater.  Okay IF the person wired it knew exactly what they were doing and it comes from the SAME circuit.

 

 

The person who did it was a qualified electrician but did not appear to understand the terms "series" and "parallel" in the contest of electrical circuits so you must judge for yourself if they knew what they were doing.  However it is beyond a shadow of a doubt the same circuit.  The wiring via the control box is the same as it was at the first attempt but connected to the fuse box side of the switch.  This places the switch in parallel with the immersion control box rather than in series as it was first time around.  I thought about this before asking for it to be done but could not think of any adverse consequences.  And nothing has gone fut so far.  Whereas if the contactor is manually energised then the controller might be able to detect this and so get confused.        

[ReedRichards]

Inside this little box is a temperature sensor which trips out if the water in the cylinder gets too hot.  The consequence of the trip is that the valve which directs water around the heating coil in the tank does not activate so you cannot reheat your DHW.  Under the black cover is a button which you can press to reset; you also need to restart the system, it seems.  I can see that you do not want to overheat the water in your cylinder but surely it is a physical impossibility for the heat pump to do this so I am struggling to understand what useful purpose this trip serves.

[dpmiller]

failed stat in the immersion heater and (IIRC) G3 compliance.

[ReedRichards]

So it's a Building Regulations requirement to guard against the unlikely eventuality that the Heat Pump managed to heat the water in the cylinder to 75 C (or whatever temperature causes the trip)?

 

Edit:  It looks like a Reliance – Single High Limit Cut-off Thermostat With Pocket (82°C)

Edited April 8, 2021 by ReedRichards

[ProDave]

8 hours ago, ReedRichards said:

So it's a Building Regulations requirement to guard against the unlikely eventuality that the Heat Pump managed to heat the water in the cylinder to 75 C (or whatever temperature causes the trip)?

 

Edit:  It looks like a Reliance – Single High Limit Cut-off Thermostat With Pocket (82°C)

Yes it's belt and braces.  I have my tank thermostat set to 65 degrees.  It never opens under normal heat pump operation, but is there to meet the regs.  There is an theoretical fault that could happen, the HP could turn on it's willis heater and the thermostat on that could have failed and it could boil the water.  Extremely unlikely but theoretically possible.

[Snoogle63]

I have just had an LG Therma v heat pump system installed. Although the DHW is set to 55deg, the hot water temperature seems to vary considerably and is sometimes not hot enough for a bath or shower. Any ideas why this is and how to rectify the problem? I’ve tried reading the controller manual and it seems there is a way of boosting the hot water quickly if the temperature isn’t high enough but I can’t seem to find out how to do this. I assume the heating takes priority over the hot water? When I got up this morning the DHW temp was displayed as 32deg despite the heating being set a bit lower overnight, the room stats being up to temp and the pump was not running. 

[ProDave]

There is a setting on mine (older version) to give priority to heating or DHW.  Mine is set to DHW priority.

 

Then there are further parameters to set DHW heating time, mine is still set to the default of 30 minutes.  There is then a wait time, how long it waits before giving the next burst of DHW heating.  the default was something silly like 90 minutes, so mine is set to 30 minutes now.

 

If the default settings in the current version are as daft as in my older version, then it will allocate only 1/4 of it's time to heat DHW meaning your re heat time after using some hot water is very long.

 

Do you have the install manual or just the user manual?

[Snoogle63]

I have the install manual but had to find the user manual online

[ProDave]

Are you happy / familliar with changing parameters?

 

the new ones have a completely different user interface to mine so I am not sure how much help I can offer, but if you list all the parameters that relate to DHW and what values they are presently set to, I might be able to make some suggestions.

[Snoogle63]

Thanks. I am wondering if there is a temperature range the DHW is set to. The controller says it’s set at 55deg but it doesn’t seem to reheat the DHW until the temp drops below 30deg. The settings are all locked so I need to get hold of the installer/commissioner, which so far has proved difficult. I don’t know how to unlock the settings to view the parameters. 

[ProDave]

There is certainly a hysteresis setting in mine, which is set to about 3 degrees.  It would be very unusual for it to be set as high as 25 degrees.

 

You need to get your installer back to unlock the settings or give you the code, then you can go through all the DHW settings with him.

[Snoogle63]

Thanks for the advice. I’ll try again to get hold of him today

[ReedRichards]

My hysteresis setting (which I did not set myself) is either 8 or 10 C; I don't remember which.  But that's okay, my hot water is set at 50 C but on leaving the cylinder it is fed through a Thermostatic Mixing Valve which brings it down to about 40 C.  Hot water has priority. 

 

I don't think it is really a secret that the code is the four digits of the software version, which you can view under settings.  Once you know the code: Menu - Setting - Press and hold the up arrow - Enter code.    

[ProDave]

I would reduce that hysterisis to no more than 5 degrees.

 

Why have the thermal mixer set to 40 degrees?  that won't be hot enough for washing up in the kitchen.

[ReedRichards]

I don't know exactly what my hot tap temperature is set at because the TMV is not calibrated - but it is about 40 C.  The TMV is not 100% accurate, the taps run notably hotter if I have heated the tank to its maximum temperature of about 78 C (using the immersion heater and "spare" electricity from my solar panels).  I know from experience in my previous house that if the tap/tank temperature was 50 C (no TMV) then my wife would complain that the hot water was too hot.  So we compromise on a temperature that is borderline hot enough for washing-up but which she does not complain about.

 

Ideally the hot water tank will not reheat after we shower in the morning so I can make maximum use of my solar electricity when it becomes sufficient around mid-morning.  In winter you are probably correct and I should reduce the hysteresis setting.  

[ProDave]

I have my hot water on a timer so it does not come on until 11AM, by which time the PV should be generating well, and then it is set to 48 degrees.  This still leaves plenty of room to heat it hotter by surplus PV in the afternoon.