HP PowerTrust A3589A Manual page 142

Troubleshooting
UPS Halted (Has No AC Output)
6-26
If the UPS returns to normal operation, that is, with the UPS
running on AC power, then it is either OK and must have entered
Automatic Bypass because the Bypass Switch Activation button was
pressed, or the UPS has an intermittent fault that occasionally puts
it in Automatic Bypass and then clears itself.
If the UPS stays in this condition—with the Service Bypass switch
in the position and after toggling the Output On/Output Off
NORMAL
switch—it is defective.
Chapter 6