I live in an 8-year old townhouse and have an A.O Smith 50 gallon hot water heater the same age. The plumber told me it needs to be replaced (does this sound like a reasonable time frame for that?) and mentioned something about a wags valve. Is this something I should have installed or is it unnecessary? The problem with the hot water heater is there is sometimes an extremely loud knocking sound and sometimes not. Thanks in advance for any help you can provide.

Wag valves (http://key8361.keyrewards.biz/prostores/servlet/-strse-112/WAGS-Valve/Detail) are not standard for water tanks... but required in some municipalities. So if you need one per the code, then you've just got to have it.

We run 400 apartments and our experience is that water tanks are funny. Some last just 5 years, some last 25.

The important question is "why" he says it needs replaced: There are many repair options available for water tanks - so ask him why he says replace it over repairing it.

Once I told him of the extremely loud knocking & that my mother thought someone was trying to break in when she heard it when she was here, he didn't really look at it & just told me if it's that loud, that it should be replaced. Would you agree with his assessment? I think I am going to have a second opinion anyway, but appreciate your input. Thanks so much.

We could tell you more if we had more details. What type of water heater do you have? Gas or electric? My bet's on gas. Is the heater flushed on a regular maintenanc schedule? In my opinion a WAG valve's a unnecessary expense. This is why we install a heater pan and drain. Nine times out of ten when a heater springs a leak it will be a small leak from a faulty weld in the boiler. In the 50 years I've been out in the field I've never seen one split down the boilers weld and dump all the water out on the fooor. As for a heaters age, I flush my heater out every month. It's the same one element, 30 gallon heater that was installed when the house was build in 1954 and is still performing with no problems. Regards, Tom

I think it is important to note that electric water heaters must be shut off by a circuit breaker or a disconnect switch at the heater BEFORE draining the tank.

Not shutting off power will allow the heating elements to overheat and burnout.

I think it is important to note that electric water heaters must be shut off by a circuit breaker or a disconnect switch at the heater BEFORE draining the tank.

Not shutting off power will allow the heating elements to overheat and burnout.

TK,
While you're correct about shutting off the circuit breaker before draining a tank you don't drain a water heater to flush it out.
For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it.
Cheers, Tom