LG Therma V 9kW – DHW Loop Not Triggering

Willits · April 20

Hello All,

I have a 9kW LG Therma V monobloc heat pump installed two years ago. I’ve hit aan issue where the unit has stopped engaging the DHW cycle, eventually falling back to the immersion heater after the programmed 30-minute delay.

The Symptoms:

Space Cooling/Heating: Works perfectly.
Cooling/Heating on - DHW call: When a DHW cycle is called, the outdoor unit remains in heating/cooling mode. The controller displays “Outdoor unit operation” and “Water pump operation.”
Fallback: After the 30-minute delay, the internal immersion heater kicks in. The display then changes to “DHW heater operation” and “Water pump operation.”
Cooling/Heating off - DHW call: When a DHW cycle is called, the outdoor unit remains idle. The controller displays “There is no monitoring information” for the first 30 minutes.
Fallback: After the 30-minute delay, the internal immersion heater kicks in. The display then changes to “DHW heater operation”.

Operation:

No Error Codes
3-Way Valve: Visually confirmed to be operating.
DHW Tank Sensor: Correctly reporting tank temperature (39°C - 42°C), so the sensor appears functional.
Flow rate: set to optimal and running between 11 and 31 lpm as needed.

I understand the only sensor for the DHW is the tank sensor. I am going to order a replacement, but it does seem odd that it reports the tank temperature but the unit does not see the input to trigger the DHW loop.

In the pics I just switched off from cooling mode, so the feed and return temps are residual from that. After a while the feed and return temps become equal.

Any advice is appreciated.

Thanks, Peter

hot_rod · April 20

the diverting turns, the pump is running? Could be an air lock in the piping between HP and tank

Willits · April 20

The diverter doesn't get the signal from the HP to switch to the DHW circuit. I tried switching over manually to make sure there was flow and its good for both the heating/cooling and DHW circuit.

hot_rod · April 20

did you check for voltage at the diverter?

Maybe the diverter motor is bad, if it has voltage and not turning?

Kaos · April 20

Do you have the wiring diagram for the unit? The unit might be looking for end of travel switch to toggle on the 3 way valve before starting DWH heat.

Jamie Hall · April 20

First thing to check is a plain vanilla loose connection somewhere in the DHW circuits…

Willits · April 21

https://forum.heatinghelp.com/discussion/comment/1894742#Comment_1894742

This is the wiring. To the DHW are 7,8,9 to the 3 way valve. The center is a common in cooling/heating mode there power to 7 and in DHW power to 9. I measure power at 7 when in cooling/heating mode, but when there is a call to DHW it does not change the power to 9. Since I get the no monitoring information message it leads me to believe an input is not working which the heat pump needs for a trigger.

The 3 way valve is a simple unit with 3 wires power to one rotates clockwise and power to another rotates counter clockwise. It has internal limit switches so it stops when fully rotated.

The big question is what. I am questioning the tank sensor CN_TH4 in the diagram, but am not so sure since I get the tank temperature on the display.

Kaos · April 21

There is no feedback on the 3 way, so that can't be the issue. If you are getting tank temperature readings, the sensor is working.

It could be that your system is set for space heat priority. It won't run a DHW cycle until space heat is satisfied and would run the resistance element instead.

If that doesn't work, maybe time for a factory reset of settings. There be dragons there, so make sure you get all the settings down before resetting.

LG Therma V 9kW – DHW Loop Not Triggering

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