The power going into the timer will be black, (Hot), and White(Neutral) using a multitester set to AC voltage 600v, will give you the voltage. Be careful when working with Live electricity.
Plastic gears in this timer. after a while the cogs on the gears get worn until they do not mesh and the timer hangs up.
try shifting the timers time 12 hours. am becomes pm then change your timer pins to the same time but from am to pm or vice versa.
this gets you using another part of the main gear and the timer might work fine. if not you will need to replace the timer.
There should be a fuse or breaker that would turn that off. It should be on one circuit by its self for the bathroom heating system. If its a breaker just flip the breaker switch.