I have H90 error on my LA-MI heat pump. What does this mean?

Modified on Wed, 22 Feb 2023 at 10:00 AM

Applicable to models:  LA6MI, LA9MI, LA12MI, LA16MI


Issue:  Error code H90 shown on the display. No heat, compressor is stopped.  


What this means: H90 error is due to a communication error between the Main Water PCB and Main Fridge PCB inside the heat pump

Action: Engineer will need to investigate by following the flow diagram below.

Heat pump must be safely isolated from mains supply before carrying out any work! 

View of main Water (aka indoor) main PCB:

The main Fridge PCB (aka outdoor PCB) is on the opposite side, closer to the fan assembly.

There are three wires connecting the two PCBs. Terminal 1 Black, Terminal 2 White and Terminal 3 Red.

Connections on the Water PCB:

Connections on the refrigerant PCB:

Malfunction Decision Conditions:

During operation of cooling and heating, the data received from outdoor unit in indoor unit signal transmission is

checked whether it is normal.


Malfunction Caused:

1 Faulty main Fridge PCB (aka Outdoor PCB).

2 Faulty main Water PCB (aka Indoor PCB).

3 PCB to PCB signal transmission error due to wrong wiring.

4 PCB to PCB signal transmission error due to breaking of wire in the connection wires between the indoor

and outdoor units.

5 PCB to PCB signal transmission error due to disturbed power supply waveform.


Abnormality Judgment:

Continue for 1 minute after operation. 


Possible parts, depending on engineer diagnosis: 

• Main Refrigerant PCB (part number depends on model of heat pump)
LA6MI part: X-2511024
LA9MI part: X-2511038
LA12MI part: X-2511044
LA16MI part: X-2511057

• Main Water PCB (part number depends on model of heat pump)

LA6MI part: X-2511031
LA9MI part: X-2511039
LA12MI part: X-2511051
LA16MI part: X-2511058

Require additional help? Please follow link below


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