SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I have a Hunter ICC 800PL controller which has been installed and successfully operating for over 10 years. The 120V circuit passes through a GFI switch. Rarely has the system tripped the GFI. Recently though, it trips it quite often (I know it is the controller because I can isolate it from the circuit). I replaced the GFI and system worked well for about 36 hours, then tripped again and cannot be reactivated as long as irrigation system circuit is included. Hunter suggested the Quick Check so I wired the irrigation circuit around the GFI and ran the test. Everything checked out fine. Irrigation system works well with this configuration.
Any ideas or suggestions?
Thanks