How is air getting into my hot water lines?
 

Right as the hot water arrives at any given faucet, there's some popping, spitting as air is released. Not a huge amount, but some. It's very consistant. I've check the meter with everything off and there is no leak. I've tried opening and closing the pressure relief valve on the water heater, too.

This is a recently installed (less than a year) electric water heater. The symptoms started not too long after it was put into service. Any ideas?

I'd check the hose connections. Usually, two somewhat flexible lines run to your heater. The connections are like garden hose connections. So.....there are a total of four screw connections. I'd turn off the power to the heater, turn off the water, relieve the pressure, then disconnect those hoses. I might use a teensy bit of silicon grease on the mating surfaces, then reattach them. Snugly.

Hopefully, Superman's suggestion will solve the problem but it's a bit of a puzzle. Since you say the problem happens at any hot water faucet, that means air must be entering the system an a point common to all--water heater is a likely spot. However, for air to enter, there needs to be a breach somewhere in the pressurized circuit and that means water should be leaking out when the hot circuit is "off." You checked the meter but a small leak may not be detected by your test method, depending on how long you had everything turned off. If you are on a slab foundation, the leak may be under the slab.

If you don't remedy the problem by tightening the connections at the heater, you may wish to call out the water company or an plumber to electronically look for a leak. Not fun but may be your only peace of mind if you can't fix it at the heater. Regardless, please let us know the results as this is a problem that we all may face some day. Good luck.

edit: One possibility may be the pressure relief valve. It may be holding pressure when the hot water is "off" but when the hot is turned "on" and pressure is reduced inside the tank, the valve seal may open slightly and allow air to be sucked into the top of the tank where it passes into the system. Never heard of that happening but it seems possible and it is something to check before you go to the expense and worry of tracking down a leak in the pipes.

The new heater could be producing hydrogen bubbles because of the anode type. That's why you would only see it on the hot supply. There are ways to test for this. The hydrogen would be flammable. It is often resolved by changing the anode type. If this is the problem, try an aluminum anode.

Yeah, my thinking is that is has to be related to the pressure relief valve. Otherwise water would be leaking OUT of any break in the line. I've checked the meter. There's a blue disk on the meter that moves at the slightest release of water. We had a trick of a slab leak a few years ago and the disk was spinning ever so slowly then.

I opened and closed the pressure relief valve a couple of times. We'll see if that makes a difference.

If you have water coming out of any faucet, the system is always above atmospheric pressure. If it was a loose connection, it would be a neat trick to allow air into the system while not letting any water out.

Never having an electric water heater, I was not aware of this. Interesting, could be the cause.

edit: Just did a quick search on the topic and, wow, it's very common. Something to follow up on, Lee.

If it is hydrogen, it will easily ignite as it is released from the faucet if you hold a flame next to it.

There is usually a warning statement right in the installation instructions.

So the air does not come out when the hot faucet is first turned on? I would suggest turning off the power to heat the water and see if it still does the air bubbles. If so then it is not the heating element. In that case somehow air is drawn back into the hot water heater/lines usually from a leaking valve or fitting. This is very evident with multi-story homes and we had this happen in our main bath shower fitting. Where the hand held was fastened to the wall pipe, water would not leak out but when I turned off the water with the shower head laying on the floor of the shower, I could hear a whistle of air in through one of the rubber seals. If I left the hand held on the hook, no air got into the system?

There is no way air is getting in a closed system, if there was a leak you would have water in unwanted places. It has to be generating air through a chemical or heating process. The anode or the heating element is the place to look.

Right. The sputtering starts when the hot water arrives, suggesting it's from the tank.

Interesting stuff about the hydrogen. I'll try killing the power and see if we're still producing gas. Guess I need to check the health of the anode rod, too.

What I was referring to was the system "appears closed" but in reality is not, i.e. air can get sucked in but water cannot get out. Since water molecules are a tad larger than air they cannot get out. We used to see this in steam condensers and finally the Navy used air to do leak tests instead of water in their main condensers. Sammy and some others may verify this although the Navy only has a few ships with "condensers" now-days!

I think turning off the power and cycling it to flush out the existing water a few times is a good test and if the bubbles disappear then you know the problem.

When was the last time you had the water turned off to the hosue and released some of that water that's still in the pipe?

Probably hasn't been done since the water heater was installed.

Air can not get sucked into a pressurized system. If an electric water heater is spurting air and there is none in your cold water, the cause is ALWAYS a burned out element. The insulation breaks down and the element makes contact with the water. Current then flows from the element through the water. This heats water just like in a steam humidifier but generates a lot of gas. If you have the skill to safely test the element with a multimeter you will see. It is almost always the lower element.

When the pressure relief is pulled, does water come out? When the heater was installed, was the tank filled while the relief was open or several hot faucets left open? If not, you could have air pockets in the tank or lines that are the cause of your problem. Also, some heaters need expansion tanks. I've never personally had one but some applications require it.

2 random thoughts:

Do you have an expansion tank on the upstream side of the heater??

How hot is the water coming out of the tank? should be 120 max at the tank and 110 at the faucet. Check with a decent chef's thermometer

http://forums.pelicanparts.com/uploa...1400348905.jpg

Problem seemed to resolve itself over time. Every now and then it pops back up (sort of like this thread), but doesn't last for long.

Ha! that's funny. I never even looked at the first post date. It showed up while I was browsing and only had a few hits so I added my .02.