I own a Mark 89 that was not regenerating and i activated the mannual regen. However, it would not stop so I did likewise and placed it in bypass. This stopped the regen. So I then placed matching sharpie marks on the time dial to determine if the timer was advancing, it was not. So I inspected the timer drive gears for worn or missing teeth, they were all fine. so I replaced the timer motor and took it out of bypass. It completed the backwash and is now running just fine. Cost – $23.54!
Good Luck, hope this helps.