DWH anode replaced

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Old 10-01-15, 11:08 AM
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DWH anode replaced

I just replaced the anode in my A.O. Smith model PGXH domestic water heater.

This is the second anode that I installed since the heater was purchased in 2000. The original warranty was for 10 years. In 2010 I checked the anode and it was showing about 8 inches of the core wire so I replaced it. Since a 10 year water heater has 2 anodes (the other is part of the supply inlet tube) I scheduled to recheck the replaceable anode after 5 years.

When I pulled the anode out this time the entire length of the core wire was exposed. There was only a trace of magnesium left on about 6 inches of the wire. Hopefully I got the new one in before much tank corrosion could occur.

I plan to replace the anode again in three years and see how long I can keep this water heater going. The anode cost $28.95 at SupplyHouse.com and is a good value compared to buying a new water heater even if the anode had to be replaced annually.

The puzzling thing is that when I drain off some of the water in the tank, very little sediment comes out. I know that there are supply tube fittings designed to cause turbulence and flush the sediment out but they require repiping the supply inlet which I am not inclined to do.

Are there any other ways of clearing the sediment from the tank? Is backflushing through the drain valve into an isolated (cold and hot water valves closed, relief valve open) and partially empty tank likely to help?
 
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Old 10-01-15, 11:45 AM
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Sediment isn't what eats the anode - it's corrosive ions in the raw water that combine, preferentially, with the magnesium atoms. I think just draining a gallon or two from the drain valve every couple of months should take care of sediment.

Are you on city water? My city water is softened at the water plant, which prolongs the life of the anode.
 
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Old 10-01-15, 03:52 PM
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I am on a municipal water system. In fact water from the Massachusetts Water Resource Authority is consistently rated one of the best in the country. MWRA treats its drinking water so that it has a pH of approximately 9.3, a slightly alkaline measurement. It is considered to be "soft" which is why I was so surprised that the anode was completely depleted in 5 years.

My concern is that sediment on the bottom of the tank will allow corrosion to occur there even though the anode is offsetting the effect of the ions in the water.
 
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Old 10-01-15, 04:02 PM
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My city water is softened at the water plant, which prolongs the life of the anode.
It depends on how they soften the water Gil... if they are using ION EXCHANGE softening, it will actually eat the anode faster.

My concern is that sediment on the bottom of the tank
Which should not be bad if you do in fact have very soft water.

The majority of the sediment that collects in water heaters is the minerals from the water, the hardness, calcium and magnesium, etc. If your water is as soft as you believe it to be, sediment should not be your big concern. If the minerals are not in the water to start with, they can't precipitate and collect in the tank! Just flush a few gallons from the bottom twice a year and fuggeddaboutit.

Yes, your water is quite soft... this data from your August 2015 report, treated, from two different stations.

Hardness 7.3 15.0 MG/L

The hardness at the second station would have to be 4 times higher to be considered 'moderately hard' water.

I am not at all surprised that an anode has been depleted in five years. That's about par IMHO. Nothing unusual there...
 

Last edited by NJT; 10-01-15 at 04:40 PM.
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Old 10-02-15, 06:47 AM
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Thanks for your feedback guys.
 
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Old 10-02-15, 07:55 AM
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It depends on how they soften the water Gil... if they are using ION EXCHANGE softening, it will actually eat the anode faster.
No, they use cold lime softening, which is a precipitate process. I'm aware that residential softeners typically use ion exchange, replacing calcium ions with sodium ions - but, as far as I know, not normally used by municipal water treatment plants.
 
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