F04 indicates that "Clamp Short" it could be anything, but the word "clamp" reminds me of a varistor / MOV, which is the component that clamps short when there is a voltage surge condition and comes back to its normal state, an open circuit, when the voltage surge is gone. Sometimes it clamps short for good when it is hit by a large surge or just by absorbing and shunting to ground many small surges.
You can brain dead the UPS to check if that resolves the issue. This brain dead test helps to reset the internal circuit of UPS.
1. Disconnect any attached load.
2. Turn off the UPS
3. Unplug the UPS from the wall socket.
4. Disconnect the UPS internal battery.
5. Push and hold the "On" button on the UPS for 5 seconds.
6. Reconnect internal battery.
7. Plug UPS in to known good power source.
8. Turn the UPS ON.
If the same issue remains even after brain dead then you have to replace the UPS. This UPS comes with 3 years of warranty, if it is under warranty you can contact APC support at 800 555 2725
If the UPS is out of warranty then you can participate in APC Trade-UPS program. APC has Trade-UPS program where in you can trade your old unit and get a new unit with great discount. You will also get a return shipping label to ship the trade-in unit to us. You can refer to the below mentioned URL.