I have an AO Smith 100-gallon water heater that's popping and
sizzling. I'm pretty sure there's a sizeable mineral deposit on
the bottom that's creating these noises and has successfully
escaped my attempts at regularly flushing the tank for the last
Is there a way, short of throwing said heater out, of getting rid
of that deposit?
There may still be life in your heater. Completely drain , open the
intake, and dump in a bottle of CLR. Wait a half hour and flush.
Inspect/replace your sacrificial rod. Of course, you'll have to plan
a time to be without hot water for a few hours.
I'm not sure they all have them. They're designed to keep the tank from
rusting. Some are screwed into the top of the tank and have hex heads.
Others are in the hot-water outlet pipe. Some have both.
Flushing is supposed to get rid of sediment, but simply draining the
tank may not work because tanks drain slowly. If you hook up a hose and
open the drain valve without turning off the cold-water supply, you'll
get a better blast to sweep sediment out.
The drawback is that if the plastic valve breaks when you twist it,
you'll get sprayed with hot water. I shut off the cold water, hook up
the hose, open a hot-water tap in the kitchen to relieve pressure, close
the tap, open the drain valve, and turn on the cold-water supply. I run
the hose to a white bucket so I can dump it every couple of gallons
until there's no more sediment. It may take only five gallons.
If I got a lot of rust I'd check the sacrificial rods.
You have deposits in your tank and need to flush it once or twice a year to
prolong the life of the heater. There are many sites on the web that deal
with this problem. Google for "hot water heater noise" and find out the
best way to flush your tank. Recently manufactured tanks do not last as
long as older models. I just replaced a 25 yo Rheem and my plumber said
that the life expectancy for newer heaters is 10-15 years, max. The
installation costs - $350 are about the same as the purchase cost for a
40 gallon gas heater.
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