LG Monobloc 12kw U32 (approx 10 years old) second hand loses controller settings on power supply interruption

[Michael_S]

LG Therma V LG HM121M.U32 (AHBW126A0)

 

So this is a second hand unit that I have installed so no warranty, no installer to fall back on.

Unit works fine unless there is even a 1s power cut after which the controller restarts in 'off' mode and the clock and programme settings are lost (it seems to go into a default 'holiday mode' settings well as being off).

 

There is no sign of a 'bios' type battery that I can see on either the controller or main unit circuit boards.

 

The unit did not come with a controller, I got a second hand one and it had this problem.  I have now got another second hand one and it at least comes back to 'on' if the power goes on and off, but it also loses the time and reverts to the holiday mode programme so is not a big step forward.

 

Can anyone advise where I can get support on this, I have not managed to find LG service support anywhere neither a phone number nor an email that gets answered.  I was wondering if I could use one of the newer controllers with my old series 2 heat pump?  It has 3 wires labelled 12v, grnd and signal.

 

Thanks for any suggestions

 

This is the controller I am using - tbh I don't actually have any documentation confirming it is the correct one for my heat pump but it looks like the pics in the manual

 

 

[ProDave]

I have a 5kW version of the same era with that same controller.

 

I concluded very early on that the controller was the most illogical thing known to man and there was no way the average "man in the street" could program that and set heating schedules etc.  So mine is controlled from the "room thermostat" input and that connects to the UFH controllers and a perfectly normal central heating time clock that everyone understands.

 

So I don't even bother to set the time on mine, let alone anything else. So I honestly can't say if forgetting the time and mode is normal or not.

 

The main thing for me is, do any parameters that you have customised remain after a power cycle?  THAT would be a right royal PITA if they all needed resetting after a power cycle.

[sharpener]

Like my 2011 Steca solar inverter it might have a supercapacitor for backup, 3V Panasonic IIRC.

 

Not very reliable, have had whole inverter replaced twice under warranty bc it failed, will try and fix it myself it it goes again as is now out of warranty.

[Michael_S]

5 minutes ago, sharpener said:

Like my 2011 Steca solar inverter it might have a supercapacitor for backup, 3V Panasonic IIRC.

 

Not very reliable, have had whole inverter replaced twice under warranty bc it failed, will try and fix it myself it it goes again as is now out of warranty.

Now that is helpful, it does have a SC on the controller board (STARCAP 0.33F 5.5v tabbed) that I had originally hoped was a battery.  Do SCs degrade over time the same way batts do in which case a like for like swap might be the answer?

[sharpener]

1 minute ago, Michael_S said:

Do SCs degrade over time the same way batts do in which case a like for like swap might be the answer?

 

I think you have probably found the solution. IIRC Farnell stocked the right one for me but I didn't want to buy one as a spare for precisely that reason.

 

Steca would not confirm it but the loss of time and date following power interruptions led me to the same conclusion. I think the first replacement inverter may have been old stock as the model had been superseded.

[Michael_S]

26 minutes ago, ProDave said:

I have a 5kW version of the same era with that same controller.

 

I concluded very early on that the controller was the most illogical thing known to man and there was no way the average "man in the street" could program that and set heating schedules etc.  So mine is controlled from the "room thermostat" input and that connects to the UFH controllers and a perfectly normal central heating time clock that everyone understands.

 

So I don't even bother to set the time on mine, let alone anything else. So I honestly can't say if forgetting the time and mode is normal or not.

 

The main thing for me is, do any parameters that you have customised remain after a power cycle?  THAT would be a right royal PITA if they all needed resetting after a power cycle.

It took me an awful long term thinking the whole unit was dodgy before I figured that this 'holiday' programme was set - the loss of any programming after each power cycle did not make it more intuitive what was going on and both the installer and user manuals are 'unclear' and limited in scope.  Luckily the service configuration settings (things like flow temp, weather comp curve etc) do seem to be retained  I guess they are stored in some sort of ROM chip.

 

Do you know if the thermostat needs to switch a nominal current (5v dc) or similar or does it switch mains voltage?  I have two wifi relays that I was going to use for thermostat control using home automation but was not sure whether to use the nominal voltage one or the mains one.  Thanks

Edited January 15 by Michael_S

[ProDave]

4 minutes ago, Michael_S said:

Do you know if the thermostat needs to switch a nominal current (5v dc) or similar or does it switch mains voltage?  I have two wifi relays that I was going to use for thermostat control using home automation but was not sure whether to use the nominal voltage one or the mains one.  Thanks

I will have to look that up.  It's a pair of contacts on the main ASHP not the controller, and you have to enable that with one of the DIP switches in the control board.

 

Do you have the installation manual for the HP itself, it should be there, if not I can photograph the relevant pages of my manual.

[Michael_S]

2 hours ago, ProDave said:

I will have to look that up.  It's a pair of contacts on the main ASHP not the controller, and you have to enable that with one of the DIP switches in the control board.

 

Do you have the installation manual for the HP itself, it should be there, if not I can photograph the relevant pages of my manual.

Yes, am aware of the dip switches and mine actually currently has a Netatmo receiver attached, I am pretty sure the Netatmo is powered by a live and return and then there is a second 'switched live' that is the 'call for heat' signal, it is just I am used to low voltage open/closed circuit thermostat controls so am just a bit wary about wiring in my mains voltage wifi switch/relay as if I am wrong it will fry the board....

Edited January 15 by Michael_S

[Michael_S]

On 15/01/2025 at 18:15, sharpener said:

Like my 2011 Steca solar inverter it might have a supercapacitor for backup, 3V Panasonic IIRC.

 

Not very reliable, have had whole inverter replaced twice under warranty bc it failed, will try and fix it myself it it goes again as is now out of warranty.

Shoots and sores, tried a replacement second hand controller, same issue of loosing setting on power off. 

 

Purchased a replacement capacitor and power cycled and settings retained.  Capacitor was 2 quid, paid a guy £35 to desolder / resolder the new one - need to develop that skill myself.

[sharpener]

21 hours ago, Michael_S said:

Purchased a replacement capacitor and power cycled and settings retained.  Capacitor was 2 quid, paid a guy £35 to desolder / resolder the new one - need to develop that skill myself.

 

Glad you fixed it. Out of interest what was the part no and where did you get it from?

 

The secret is a good de-soldering gun (solder sucker), I only have a manual one which IIRC came from a firm I worked for at one point, the professionals now use ones with a little vacuum pump that runs continuously.

 

The £35 made me wince a bit having just repaired some tricky broken wires inside my son's digital alarm clock. Now I know the going rate I can bargain with him for fun and profit. Previously his teacher g/f's hair curlers needed a new ballast resistor, the school science technician had had a go and made it a lot worse by stripping the track off the pcb.