Plumbing in the Home/Water Heater question


I've got two gas hot water heaters (A.O. Smith  40 gallon), and one of them needs the pressure valve replaced.  I THINK the two water heaters are hooked up in series, but they may well be hooked up parallel.  
I know replace the temp/pressure relief valve...I need to: (1.) Turn off the gas, 2.) Turn off the cold water inlet, and then (3.) Release a little water out of the reservoir via the bottom spigot just to be safe.  
My question:  To replace the pressure valve on just one of the hot water heaters, do I need to release pressure and water from BOTH of them?  (I know I'll need to turn off the gas and cold water to both.)  And does the correct procedure change between a series vs. parallel connection?

You don't really need to shut off the gas, just lower it to the vacation setting on the round dial at the bottom.  Makes cranking it back up so much easier and you just turn the knob back to where you want it.

You DO need to turn the water off and seeing as WE DO NOT KNOW how they are hooked up, then safe to turn BOTH the valves off on both heaters. Then go inside the house and turn on a couple of the faucets hot sides and make sure the water IS INDEED not on, as not all valves actually work just because they seem to turn off.

Also, make sure NO ONE is running water inside, as if someone opens up a faucet while you're working on this thing, cold water can backfeed into the hot side, RE-PRESSURIZING THE SYSTEM!!!

As far as draining?  I never do.  It takes about 5 seconds to unscrew this thing and screw in another. Just don't get nervous and if you're of the faint of heart....then drain it.  But with the valves off, the water that comes out can easily be cleaned with a towel and will cause no harm at all.  It comes out like....balook, balook, balook, cause there's no air behind it.

But....if you really want to drain it, go ahead, but not worth all the trouble.  I don't even drain electric heaters when installing elements...if that tells you anything :)

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