That has never been flushed before? You know how when you flush out the fluid in an automatic transmission with over 100K miles that has never been flushed, often the next thing you have to do is replace the "tranny" because some of the sludge was actually holding things together. I know that sounds whacked out, but I've seen it happen many times. I don't want to flush my two 40 gallon heaters and open a "can of worms" as it were. For example, one possibility that comes to mind is that the sludge in the bottom of my water heater has rusted out or compromised the lining of the tank, and if it is dislodged, it may pull away some of the old and weak lining and cause a leak. Anyone have any experience with this?

I don't know about transmissions but if your boiler is containing 45 to 60 PSI I wouldn't hesitant to flush it. However if the gunk has built up over the boiler drain and blocked the inlet you may have to unscrew the boiler drain and stir it up with a rod to loosen the gunk up so it will flow.
There's a downside to this operation. You have a 40 gallon head of water that will be draining out on your floor unless you're very quick about screwing the boiler drain back in. If you have to remove the boiler drain don't forget to shut the water off to the heater. Good luck and happy flushing. Tom

It is possible that the build up in the tanks is in part keeping them from leaking. Flush at your own risk. 20 years is far past the life expectancy of a H20 tank and I would start making provisions to replace them anyway. Also I typically hook up my garden hose, shut off the water, open the biler drain at the bottom of the tank and then turn the water back on to blow out the build up from the boiler drain. I would not remove the boiler drain at the bottom unless necessary as you may not get it or a new one back on. Good Luck!

Hey Loken,
I was beginning to take you serious until I ran across this.

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It is possible that the build up in the tanks is in part keeping them from leaking. Flush at your own risk.

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I would like you to explain how sediment and gunk would patch a leak in the tank that's holding anywhere from 45 to 60 PSI. And while you're at please explain how open the boiler drain and flushing out the gunk would cause a lea?

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20 years is far past the life expectancy of a H20 tank

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How about a 30 gallon single element water heater that's over 55 years old? I have a under the counter heater that was built in when my place was built in 1954 and still going strong. Since it's located on a outside wall I extended the boiler drain outside and every month or so simply open the valve until it runs clear.
So much for flushing at your own risk. Or perhaps the tank split a weld and all the built up gunk is containing the pressure.

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I would not remove the boiler drain at the bottom unless necessary as you may not get it or a new one back on

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While I don't recommend removing the boiler drain myself I fall to see how removing it would screw up the threads so bad that it couldn't be replaced. Cheers and giggles, Tom

Nice on the 50 year old tank. As far as I have seen the electric tanks tend to out live the Natural Gas 2-3 fold. In my experience a lot of water tank drains are plastic anymore and tend to break off in the tank when removed. Now for a good plumber like you that would not be a problem to chisel out the old drain and put in Brass but for the average Joe this may be more difficult.

On a few occasions I have drained tanks for clients only to be replacing them a few days later. I understand your point about the pressure and how that doesn't add up perhaps just coincidence. I guess its not two hard to believe that a tank with several inches of build up/sediment would have a partially corroded/expired liner as well. I guess there would be other considerations to like brand and age etc. Hot water tanks just are not as good as they used to be.

Loken,
Thanks for your imput. In the future please use the EDIT button to add tom your post. Starting a new back to back post just makes more work for me. And don't forget to check the date in the upper left hand corner before you post. Thanks, Tom