Thank you for including timer model number.
You have almond-colored ST01AC timer that worked before and then stopped working.
The manual override no longer turns lights on-and-off.
Manual override works by pushing in timer door, and also by pushing on-off button on face of timer.
1) Try pushing on-off button directly instead of timer door, in case little plastic point on timer door has worn down. If timer door is worn down, maybe add a few layers of tape so door can push button again.
2) If timer on-off button is not working, then timer may be defective -or- timer CR2 battery needs to be replaced, and then timer reset and reprogrammed.
3) Defective timer: timer has 1 year limited warranty against workmanship defecthttp://www.intermatic.com/customer%20service.aspx
4) Replace CR2 battery, reset timer, and reprogram timer and see if functionality is restored.
If timer is not restored, then timer is going bad.
Open following link for illustration of battery replacement, steps for resetting timer, and illustrated re-programming steps.
5) Take a moment and rate answer:
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