A few things I've noticed with the timer component (Pega SP1 8.0.2003.0):
1. If I call Stop/Start/ResetState or change the enabled property to False, The timer will never fire another tick event even if I call Start or change the enabled property back to True.
2. The enabled property is disabled by default. Change that to true before debugging.
Suggestion, create another global variable for handling the Timer enabled/disabled usage and place it directly after the tick event. Your timer event will always fire, but the variable flag will determine if it should continue the thread or not.