I have narrowed the problem down to the power exhaust is not working. I can not tell if it is the blower motor or selanoid switch. I have a second identical water heater which I used to swap out parts until I found the gerneral area that was bad. When I swapped the exhaust fan unit that fixed the issue. How can I determine if it is the vacuum switch, selanoid or the motor. The motor blades turn freely and I can not find any areas that look like any part was ever hot or even warm. Still need parts so I can have two water hearters working again. Thanks, in advance, for your help