HIGHError Code
U2: Serial Communication Error (Heat Pump)
Mitsubishi heat pump communication lost between indoor and outdoor units.
What This Error Code Means
Indoor and outdoor control boards cannot communicate via the serial data line.
Common Causes
Wiring between units damaged
Loose terminal connection
Control board failure
Voltage surge damage
Rodent damage to communication wire
Affected Brands
MitsubishiDaikinFujitsuLGSamsung
How ROMA Heating Fixes This Error Code
Inspect communication wiring
Check for loose connections
Measure voltage on communication lines
Test each control board independently
Replace failed wiring or boards
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