There are two questions I need to ask. You probably know all about the first question. Is the cover properly installed when you are getting a supervisory signal back at the panel? Switch S1 is a tamper switch for the tamper switch (not really redundant wording). The Potter PTS-C will send a trouble signal as long as the cover for the switch is not secure.
The second question is based on the actual plug-in tamper mechanism. Was the extra tamper cover removed when the plug was reinserted?
Information on this tamper switch can be found at:
Once the plug is removed from the switch, an extra step is required to make sure an unauthorized person hasn't just closed the valve and put the tamper back. This is copy-pasted from the instruction sheet.
"Turning the valve wheel will pull the plug out of the receptacle. The plug cannot be reinserted after operation until the plug receptacle cover is removed with the special hex key provided. This key should be left with the building owner or responsible party. Replacement or additional cover tamper screws and hex keys are available. For cover tamper screws, order stock no. 5490344. For hex key, order stock no. 5250062."
The cover is on the right-hand side and uses a tamper-resistant screw to stay closed. Once the cover is removed, it should be obvious how the plug can be reinserted. Until that extra cover is removed, and the mechanism is reset inside it, the tamper switch will continue to send a Supervisory Signal back to the fire alarm control panel.
The sprinkler company will have lots of the needed Tamper Allen Wrenches. You might try Home Depot or other contractor's stores to get a Tamper Allen Wrench if you need one in a hurry.