3) The indoor main PCB damage.
Solution: Replace the indoor main PCB. 
10.5.3 Display E3, E7 
Reasons: 
1) Outdoor pipe temp sensor, outdoor temp sensor & exhaust temp sensor connection terminal loose or not
plugged in.
Solution: Check the connecter of sensor and slot, if loose or not plugged in, please connect again. 
2) Outdoor pipe temp sensor, outdoor temp sensor & exhaust temp sensor damage (short or broken).
Solution: Check and replace the sensor. 
3) Outdoor PCB damage.
Solution: Check and replace the outdoor PCB.
10.5.4 Display E8 
Reasons: 
1) Outdoor discharge pipe temp sensor connection terminal loose or not plugged in.