Loud popping sounds from water heater after pipes have been drained

[Neil.Steiner]

I drained my water pipes because I need to replace a failing saddle valve on the hot side with a proper Tee and quarter-turn valve.

I began by turning off power to the water heater, turning off the water main, opening all faucets starting from the top of the house and working my way down. The pipes coming out of the WH are higher than the basin whose faucets I opened last, so there should still be some water in the WH inlet and outlet, unless a lot of it was syphoned out.

Somewhat sporadically, but perhaps every 30-300 seconds, I hear a loud pop from the WH, and this has been going on for at least 30 minutes. The WH is much older than I'm willing to admit, but I flush it every year, and don't recall ever hearing loud pops like this before. Much too loud to be drops of water, but that leaves me completely baffled as to what it could be. If the tank was failing, I wouldn't expect the sounds to go on and on. I understand that the tank will gradually cool off, but the popping didn't begin until I drained the water from my system. (I can't upload a sample because this forum doesn't accept .mp3 files.) Under normal operation, the WH never makes much noise.

[I turned off power to the WH by flipping the breaker, and verifying that the input now reads 0V, where it previously read ~240V. I just now double-checked again that voltage is 0V, and I carefully shorted the terminals to prove to myself that I'm not mistaken.]

Any thoughts on what this might be? I replaced the WH TPR valve about a year or so ago, I periodically replace the anode as needed, and have otherwise had no problems with it. When I flush it, the sediment is never very bad.

 

[Plumber69]

The vacuum breaker, gulping air

 

[Sponsor]

 

[WorthFlorida]

You have fairly cold water inside from an empty tank fill and mineral deposits are on the old heating elements. The heating elements are staying on longer than normal and water that is under the mineral deposits are turning to steam. This is very common with gas water heaters and the steam does condense back water. Similar to a tea kettle that is normally used to boil water, it seems to gurgle before boiling.

 

[Neil.Steiner]

@plumber69, thanks. I take it this may be something internal to the tank? I ask that because the only things on the top are the inlet, outlet, TPR, and anode bolt, and the only thing on the bottom is the flush valve. In any case, I finished the repair, and everything seems to be working fine, so you are probably correct. Thanks for reassuring this DIYer.

 

[Neil.Steiner]

@WorthFlorida, this is actually an electric heater, and I didn't empty it before my repair (just drained the other pipes in the house), so when I turned the main back on, the water coming out of the tank was still very warm. You could still be right about sediment on the heating elements—I've never checked them—but I know that I get fairly little sediment out when I flush the tank. So who knows?

 

[Tuttles Revenge]

You might want to verify that your breakers are working. Zinsco (sp?) panels/breakers are notorious for being energized while they are switched off.

When you drain or partially drain an energized water heater at some point the water begins to boil and makes loud noises.

 

[Jadnashua]

Before turning on any water heater, make sure to open a tap somewhere until you get all of the air out.