A Network Fault is a problem (Trouble) with the fire alarm system. The fault has to be fixed before it can be cleared from the panel. To clear the trouble from the display, there's also a trouble memory that requires the troubles to be acknowledged and cleared after fixing the trouble.
There is also a front panel key switch. This allows the buttons to be used, or "enabled". Make sure that switch is enabled, or the buttons will not do anything.
If there's other troubles, one that you have to scroll through, go to them with your voltmeter and check for voltage at the connections. Check everything before trying to replace parts. Usually, the problem won't be quite as obvious as what the panel is saying.
With most fire alarm systems, the term "Network Fault" means either a wire is broken somewhere else in the building, or another piece of equipment isn't communicating.
A manual on the FCI-7100 can be found at:
The manual is very helpful.
After you have checked out everything in detail, including using the voltmeter, then check with Technical Support for the fire alarm panel. Find out what they have to say. Helping you is the reason they're there.