After having our gas hot water tank replaced, when we turn off the water it makes a lilttle banging noise, is there air in line, and how to drain air from line? Thanks, mh

Did the plumber flush out or bleed all the faucets when he completed the heater install? Just run each faucet for about 20 seconds and that should bleed out any air. Actually the symptoms reflect a loose pipe or lack of thermal expansion tank. Did the plumber install a thermal expansion tank. In many areas that is required now. The faucet you are turning off and getting the noise, does the noise only happen there or at other places? You may have a faucet that needs attention too.

It happens when we run and then turn off the hot water faucets, dishwasher, etc. I live in northeast Pennsylvania and I don't think it's a thermal expansion tank. But there is a water pressure valve installed on tank with a long pipe.

Also, I do not remember him bleeding or turning off the faucets to let air escape.

If I let the faucets run for 20 seconds, do I do only the Hot Water Faucets, and must I first turn off the water main that is in basement? Thanks so much, m.h. near scranton, pa.

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Originally Posted by m12345

after having our gas hot water tank replaced, when we turn off the water it makes a lilttle banging noise, is there air in line, and how to drain air from line? thanks, mh

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If you do not flush,(not drain) your heater on a regular basis it will build up mineral on the bottom of the tank. When the flame comes on it turns the water trapped under the mineral to steam and the steam escaping is what you hear. Let me show you how to flush your heater. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) and some white grains,(lime or calcium carbonate). The whole thing shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. . If the problem still persists after you have flushed, you will have to drain the heater, remove the boiler drain and go up in the bottom of the tank with a wood or plastic rod, (not metal) and try to break up the mineral and flush it out.

If that don't get it then recharge your air chambers.
"Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in shock absorbers,(air chambers) to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatorys and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will begain to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out TOM

Mh, I would guess that since you have had the heater installed you would by now have bled all the air out. I am going to rule out air in the lines. And seeing that you have a new heater I am going to rule out mineral deposits on the bottom of the heater. And since it appears the problem is on the hot water side only and if there are air chambers in your home they would have been recharged when the heater was drained and the water was off, so I am going to rule out air chambers too. I am back to the expansion tank as a better shock absorber or a faucet problem or loose pipes. It is doubtful that the installer loosened some pipes and you did not have this problem before the tank was changed out, correct? And am I correct is reading that it only happens on the hot side? How much pressure [psi] is on the water system?
Frankly I am puzzled by this question. It has been my experience that banging noises are from a few sources. A toilet that has the old float that is almost turning off will chatter or bang when worn out. Usually a bad flapper is the cause. Pipes that are not strapped well will sometimes make a banging noise but this would be hot or cold, and this would only happen with sudden stops from fixtures that close quickly or have a solenoid type shut off like a washing machine or dishwasher or a fluidmaster toilet filler, and usually this is associated with high pressure. In atlanta we have very high pressure because of all the hills and valleys. The average street pressure is 146 psi. anything over 85 psi requires a pressure reducing valve [prv] and they come set at 50 psi. a good working pressure is from 50 psi up to 65 psi. when a prv is failing or has failed it will hum or chatter.
After taking all this time to say all that, I still am not comfortable that I have identified your problem. But I feel that an expansion tank will probably help considerably if not solve it altogether. An expansion tank is 30 dollars at home depot or Lowe's and it should be adequately supported and installed somewhere on the cold pipe. Typically it is installed on the water heater area. It would serve best near the end of the system, but could probably be installed anywhere on the cold side. If you can install it, it should take about 45 minutes to shut down the system, drain it, install it, and restore the system.

Doug, I lilke your answers best. There is a new pressure reducing valve and pipe on new water heater. When I turn any hot water faucet off SLOWLY the noise does not happen. I did let the hot water run on the furthest faucet (2nd floor) for about 5 minutes, but have yet to really pay attention to see if it stopped the banging sound. Will listen carefully when the family is awake and using it. Thanks, like I said, I like your answers best, you really listen. Marie h.

Please check out this site Pressure Regulator Valves - Keidel Bath, Plumbing, Kitchens - Cincinnati, OH
It appears as if you are looking at the temperature and pressure relief valve [T & P ] on the water heater and calling it a prv. If you can, get a test gauge that fits on an outside faucet and check the pressure on every outside faucet.
Please read this article about thermal expansion tanks to see why they are required
Sizing Thermal Expansion Tanks - Feature Article - PM Engineer

DOUG-- I will buy this test gauge, but do you mean to test it outside the house before the water comes into home, because if so, it is freezing out here in northeast PA. and our outside faucets are turned off, so would I have to wait till its above freezing to do this test? Thanks again, m.h.

Mh, the first thing I would like to know is the pressure on the water system. The common way to check it would either be an outside faucet or the faucet at the washing machine. If you have a brass drain on your water heater you can flush it out a bit to avoid rust and test there. Next, this noise, is it more of a chatter like a machine gun? Have you peeked inside the toilet tanks when this noise happens? If the toilet is chattering then turn the valve under that toilet off and see if that helps. This way we can eliminate things as we test.

I do know: there is no burst of air or spurting water from any faucet in house. The toilet, when flushed, does not make noise! It does actually sound like one of the pipes going into water heater, but I would probably have to be in basement near the water heater to check when someone uses faucets, am I correct? My husband doesn't notice the sound, and said to not bother about it.

Hopefully you can be in the basement when this happens so we can better identify it