Equipped with fully automated control systems, this device automatically performs the required back wash and regeneration processes at certain intervals, as determined by a program that is configured at the beginning, at any time, without the need for human intervention. Specifications Time-controlled back wash. The first two numbers in the serial number, which may appear after one or two letters, are the year of manufacture of an A.O. Smith water heater. So the data plates shown below indicate that the water heaters were manufactured in.