Oil fired hot water heater "popping sounds" Mag oxides from anode?

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keene, nh
I have a standard residential (thermaflo 30 gal) oil fired hot water heater that about 9 years old. I replaced the anode 4 years ago and again last year and it was about half corroded away. The water heater has no issues other than an irritating "popping sound" near the end of the firing cycle.

The heater provides a single apartment's hot water and it has a circulatory tube in tube home-made copper heat exchanger that provides radiant underfloor heat to a ~800SF apartment. The heating loop uses Radiantec 7/8" cross-linked poly and it's worked just fine now for 18 years. The only reason I mention this is because during cold weather, it runs almost continuously (as it's supposed to) it is extremely economical and I'm happy with it. But because it's used for heating it cycles fairly frequently, but appropriately.

Near the end of the firing cycle it "pops" (pop-pop-pop) for a minute or two. I suspect that it's a build-up of magnesium oxides laying on the bottom of the heater. I always put a full bore drain valve and when I drain some water when it's popping I do see some sediment. I'm wondering if there is any way to actually totally clean out this sediment?

I dropped the temperature from 130 to 120 f thinking that the thermostat might have "aged up," but it still "pops." I doubt that it will affect the life of the heater and suspect it's more an irritant but it would be nice to get it to stop. Any ideas?

We have no calcium/lime build-up here. It's city water and chlorinated. (NH)

I do realize that 9 years is "pushing it," but I often get 12-14 years for a bock or thermaflo since I replace the anodes.

Have any of you ever dealt with this? I wonder if draining it and using a brush through the drain hole, then angling it sideways and using a hose from the top might work to clean any sediment.

Or might there be another reason for the popping sound? I have verified that the outgoing temperature is currently ~120f.



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To improve cleaning, replace your drain valve with a full port valve. I replaced my plastic drain valve with several parts: nipple, full flow drain valve, GHT adapter. There is now available a brass full flow drain valve, which I would have used instead:
  • Rheem AP12231C-1 Overall Length (in.): 6-1/8
  • Rheem AP12231B-1 Overall Length (in.): 3-3/4
Now that I think of it, I wonder about the difference between "full port" and "full flow". If you get one of those Rheem valves, could you post the ID -- how big of dowel or drill bit would pass through? With full port, I would expect a 3/4 inch rod to pass through.

They have wands to help squirt water. The Camco 40103 is 25.5 inches long. https://www.campingworld.com/water-heater-tank-rinser https://www.walmart.com/ip/Camco-RV-Water-Heater-Tank-Rinser/29764286 I have thought that an electric pressure washer with a small enough nozzle could be effective. I don't know what the risk of damage from too strong of a spray would be. Maybe the nozzle could be unscrewed, and the flow from the tube would be enough. Take pictures and post successes if you do something like that.
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Retired Defense Industry Engineer xxx
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New England
Sometimes you can get mineral deposits on the lining of the tank. If they're next to the burner, because they can act like an insulator, the water inside of them can boil and make some sounds because they can heat up much more than the water in the rest of the tank - micro steam explosions.

Are you able to view the burner when this occurs? Does the flame stop abruptly, or does it sputter a bit when shutting off?
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