Reset timer by holding down on-off button then press and release small round reset button. Then release on-off button. Display should flash 12:00
This timer uses CR2 battery.
If functionality is not restored after new battery and reset, then timer has probably gone bad?
http://waterheatertimer.org/ST01C-program.html
ST01 timer has 1 year warranty from intermatic.com
gene
h If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7
Mine sometimes switches itself (!) From AUTO or PGM to SETUP. Simply use your fingernail to open top of door/switch and touch "Mode" button until it reads PGM or AUTO or MAN, as you wish.
Add a comment with more information:1) Brand and model number of fan and remote so expert can access product manual. Without product manual, we're guessing. If product manual has a phone number call it.2) Attach clear in-focus photo of existing switch with all wires for best possible guess.3) get a tester and find which wire inside the box is hot. Turn off switch and test each black wire to bare ground wire.Geneh If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7
Intermatic does not post schematic for ST01C timer, and I have not taken my timer apart to see if a gear is loose.http://waterheatertimer.org/Intermatic-timers-and-manuals.htmlAdd a comment and describe timer in detail. Attach a photo.Buy another timer and do not take apart, since these timers are sealed to meet UL electrical and fire-shock safety standards. If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7