EG4 › FlexBOSS21 DC-DC converter board
FlexBOSS21 shows Battery open fault, W027
reported more than once
Symptoms
- Solar production intermittently drops by roughly 20% around midday on many days, sometimes recoverable by restarting the inverter, with one internal radiator temperature sensor running notably hotter than the others at the time of the drop
- Separately, a growing wave of RMAs traces to the DC-DC converter board burning out and disconnecting from the battery outright, throwing a non-recovering 'W027: Battery open fault' while grid-to-load power and PV production keep passing through
Alerts and codes
W027: Battery open fault (FlexBOSS21 DC-DC converter defect)
The cause and the fix
Subscribers see the cause, the fixes that worked and who did them, part numbers and recent prices when a part is involved, and the field reports behind this entry.