Gas heater making boiling noises

[LLigetfa]

I've got a 3 year old Reliance GSW rental tank - gas - power vent - 6G40NVH-FV-02 - B4743 that has started making thumping noises. Best as I can tell, the water is on the verge of boiling... vapour bubbles form and then quickly condense. It didn't always do this and it's getting annoying. It started after the gas valve was replaced but don't know if it's related. Just one more noise in a long list of noises. Water temp is the same as always.

[jadnashua]

Could be mineral deposits...

[BizzyBeePlumbing]

I would pull the drain valve, install a 3/4" nipple and a ball valve and flush the unit. Jim is probably right, sediment in the bottom of the tank

[LLigetfa]

Could be mineral deposits...

Ja, that crossed my mind. I'm thinking that they are probably like potato chips though that flaked off and would not flush out the drain even if I changed it out to a full port ball valve. Probably not as bad as the following classic pic. I've opened the cheap plastic drain and only clear water comes out.

I found this how-to that calls for a tube to be inserted like liposuction.
http://waterheatertimer.org/Clean-se...er-heater.html

[jadnashua]

If water can't flow (convection) over an area that is being heated because a little is trapped behind a mineral deposit, eventually it will flash into steam, break through that little mineral bubble, and make noises. The more mineral deposits, the more this happens. That mini steam explosion takes its toll eventually, but is mostly annoying.

[Runs with bison]

I've got a 3 year old Reliance GSW rental tank - gas - power vent - 6G40NVH-FV-02 - B4743 that has started making thumping noises. Best as I can tell, the water is on the verge of boiling... vapour bubbles form and then quickly condense. It didn't always do this and it's getting annoying. It started after the gas valve was replaced but don't know if it's related. Just one more noise in a long list of noises. Water temp is the same as always.

How hard is the water?

What is the temp set point?

I'll take your word for it that this is incipient (or full fledged) boiling with normal conditions. We had extremely hard water when I was a kid and as the oldest I used a long handled spoon to scrape out a lot of insoluble carbonate (retrograde solubility of various compounds) both at home and at the water heater in the dairy barn. Although I did a couple of electric element replacements the tanks were still running when I graduated from college and went my own way.

Retrograde solubility is a bitch. Magnesium and calcium carbonates actually precipitate as temp increases--the opposite of normal behaviour where most materials become more soluble with temp. If you have soft water , (as I had on moving to Texas) you will be asking: "What the hell is he talking about???"

[LLigetfa]

I don't recall the numbers but I have hard water. The old State tank sprung a leak after 10 years and it was very slow to drain so I'm guessing it was pretty crudded up. I tried to trip the TPR at the time thinking I'd break the vacuum to drain faster but it turned out to be all crudded up and wouldn't move.

Not sure about the temp set point but it is higher than the default. A 50/50 mix of hot and cold is about right for filling the wife's soaker tub.

I did the math and figured I'd break even renting versus buying if it only lasts 10 years. The only thing I didn't think through is if it lasts much longer and fills up with scale like the pic above and the rental company doesn't want to replace it. Then I'd have to cancel and buy a new tank or go tankless.

[jadnashua]

If a tank gets that full of deposits, it wouldn't provide much hot water and that alone, rather than a leak, should consitute a valid reason to replace it. You'd have to read the fine print carefully, though.