One morning the graphs of my heat pump shot up to 1200 °C. Flow and return, both of them. My LG Therma V reporting 1200 °C is not a heat pump running wild; it is an error value. But without countermeasures it ruins your graphs and your COP for months.
Where the 1200 °C comes from
When the Control Unit of the LG Therma V R290 has no contact with the outdoor unit, it returns fixed values via Modbus:
| Value | What the LG reports |
|---|---|
| Error code | 237 |
| Flow and return | 1200.0 °C (raw 12000) |
| Outdoor temperature | 25.5 °C |
I also saw −64.9 and 300.0 °C on sensors that do not exist on this unit.
Why cleaning up afterwards does not work
My first reaction was to wipe the wrong values from the database with recorder.purge_entities. The graphs kept running up to 1200 °C. That service clears the normal history, but not the long-term statistics that the graphs draw on for longer periods.
The fix: never let the LG Therma V 1200 value in
The Home Assistant Modbus integration has the nan_value option: a raw value that means “not available”. If the sensor receives that value, it becomes unavailable instead of 1200. An example for the flow temperature:
modbus:
- name: lg_therma_v
type: serial
port: !secret lg_heatpump_modbus_port
baudrate: 9600
bytesize: 8
parity: N
stopbits: 1
sensors:
- name: hp_outlet_temp
slave: 33
address: 3
input_type: input
scale: 0.1
precision: 1
unit_of_measurement: "°C"
device_class: temperature
nan_value: 12000Check addresses and scale against the Modbus documentation for your model. In addition:
- The heat pump graphs have a fixed y-axis, so an outlier that still gets through does not flatten the rest.
- The COP calculation does not use unavailable values.
More status messages from the LG that you should not blindly believe: which status bits you should not trust. All incidents: Lessons from practice (in Dutch).
These values apply to one installation. Check them against your own documentation; leave work on 230/400 V to a qualified electrician.
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