New water heater banging away…

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    • #277159
      Avatar photoGarrett Lane

        Hello everyone,

        We just had a new Hotpoint 40 gallon, gas, direct vent
        water heater installed.

        When the cold water is shut off anywhere in the
        house, by us or an appliance, a loud metallic bang can be
        heard coming from the water heater, followed
        by three or four additional knocks which get softer until they
        stop. It sounds like something is swinging inside
        the water heater and hitting something over and
        over again.

        No noise is heard when the hot water, or a mixture
        of hot and cold water is shut off. Only straight cold water.

        Could the drip tube be smashing into something, or do you have
        any other ideas?

        Thanks for the help!

        » This message has been edited by UTahJ on 28 January 2004

      • #295566
        Avatar phototurdchaser

          Most likely one of two things,
          First and most common is a valve that is not completely closing. Turn the water off to the clotheswasher and see if it goes away, then turn the water of to the toilets and see if it changes. If this does not isolate it the next most common possibility is that you have a closed domestic water system. Being that there is either a backflow preventor or pressure regulator on the incoming line. As water heats up in the tank it expands and pressure buildsup because it can not desipate into the water supply system because it is closed. The excess pressure will make all sorts of noise when valves are operated. Most likely the first scenario will fit. Let us know!

        • #295567
          Avatar photoUTahJ

            Thank you for the reply.

            I tried turning off the supply to the washing machine,
            and the toilet separately, and then I tried them together.
            (we don’t have anything else that would use cold water
            other than the kitchen and bathroom faucets), but the
            banging in the water heater persisted.

            It appears to be a closed loop system as you stated,
            however there isn’t a pressure regulator or backflow
            preventor visible inside the house. The line exits
            through the basement floor and runs about 20 feet
            to the city shut off valve in the front yard. And the rest
            of the system is just plain old copper pipe.

            The noise wasn’t present with the old water heater
            we had, but that thing wasn’t very efficient either, so
            maybe thermal expansion wasn’t an issue.

            Any other suggestion?

          • #295568
            Avatar photoSelgas

              Fairly certain that your problem is related to a loose fitting pipe on your water line somewhere that is not properly clipped or strapped.
              Simply, when you close a tap under mains pressure the shock wave causes a vibration we call water hammer within pipes on ocassions. This is usually more commonplace with appliances that have fast opening or closing solenoid valve that “slam” shut causing the shock wave in the piping system. If you cannot locate the loose pipe you can fit a device into the water line called a water hammer arrestor that will do the job for you.
              You should also check and make sure that the water heater has a pressure limiting valve fitted on the inlet cold water line to it – the purpose of this device is to ensure that water pressure does not exceed that to which the water heater relief valve has been set, thereby no stressing any other valves within the system.

              Selgas Services Ltd
              Craftsman Gasfitters, Plumbers, Electrical Service Technicians

            • #295569
              Avatar photoUTahJ

                Thanks for the reply Peter.

                The noise is definitely coming from inside the
                water heater. I don’t hear any noises from the
                rest of the piping in the system.

                I tried putting the smaller, bladder type, water
                hammer arrestors on the toilet, kitchen sink,
                and the washing machine cold water lines this evening,
                but they didn’t do a darn thing. Maybe I should
                have tried them on the hot water side, but I got
                discouraged by the inital results on the cold side.

                You’re idea about a pressure limiting valve on
                the hot water inlet might be my only choice.
                My only concern is that I played around with adjusting
                the cold water inlet valve on the water heater, to
                see if I could eliminate the bang. The only time
                it disappeared was when the cold water was almost
                all the way off, thereby reducing our hot water pressure.

                I’ll check into the value though… I’m sure what ever
                is making the noise in the water heater is bound to
                break eventually… not a good thing.

                Thanks again!

              • #295570
                Avatar photoDUNBAR

         <<<< click on products, then thermal expansion..........this is a recommended item on a closed system.
                  Once you know your water pressure, then make the decision to go with the PRV………which should be on the main water line immediately following the main shut off valve to protect the entire plumbing system, hot and cold.

                  » This message has been edited by DUNBAR on 29 January 2004

                • #295571
                  Avatar phototurdchaser

                    The next step I would take is to turn the gas off and run water to let the tank cool down. Then see if the problem is still there, this will give us an idea if the cause is coming from outside of the water heater or is being generated from inside the tank.

                  • #295572
                    Avatar photoUTahJ


                      I liked your idea, so I tried it as soon as I got
                      home. I shut off the water heater and ran the hot
                      water until it ran cold. Guess what… same noise.
                      I guess that rules out thermal expansion problems.

                      So I’m assuming I have water pressure that’s high
                      enough to make something in my hot water heater rattle
                      around when a faucet is turned off.

                      Two more questions before I call the plumber back:

                      1. If I had to turn the cold water supply to the water
                      heater almost all the way off before the bang stopped,
                      wouldn’t I have to set the pressure reducing valve
                      to such a low PSI that it would be unbearable, just
                      to acheive the same effect?

                      2. What are the odds that the water heater we purchased
                      is just faulty, with something loose inside?

                      Thanks for everyone’s help!

                    • #295573
                      Avatar phototurdchaser

                        Yes, exactly. We have eliminated thermal expansion as well as the noise that air escaping from the water in a gas water heater makes as it heats up. The likelyhood of the tank being faulty and causing it is low. It is possible but very unlikely. Personnally I have had guys drop tanks and there be visible damage to the outside. I have turned around and sold them at a loss and personnally backed up the warranty and have yet Had a problem with one. This is why I say it is possible but unlikely. Have the plumber inspect the water supply piping for any causes and if none are found the following product is your best bet to fixing the problem. It should be installed on the cold water supply just before the tank.
                        click on homeowner general info., click products red button, click residential, expansion tanks then therm-X-Trol
                        Do let us know how it turns out when you get it fixed.

                        » This message has been edited by turdchaser on 30 January 2004

                      • #295574
                        Avatar photoSelgas

                          Ahhhhhh ha from your last post I would not be surprised to find the fault being a broken off or very loose hanging anode rod or dipper tube in the cylinder itself – if these were at fault then the noise would only be evident when hot water was being run or when a hot tap was turned off.
                          These problems on a new cylinder would indicate to me that it had been mistreated when being transported. Both of these components can be easily changed or checked as they either screw into the cylinder or fit inside one of the water connections.
                          The problem you have explained is less likely to to be pressure related but more something amiss within the tank itself.

                          Selgas Services Ltd
                          Craftsman Gasfitters, Plumbers, Electrical Service Technicians

                        • #295575
                          Avatar photoUTahJ


                            It sure sounds like the anode rod is hitting something,
                            because it is definitely a metal on metal sound, but
                            it doesn’t happen when the hot water is used, or
                            when hot water is mixed with cold. It only happens
                            when cold water is used.

                            Most drip tubes are plastic now, aren’t they?

                            Thanks again!

                          • #295576
                            Avatar phototurdchaser

                              All dip tubes are plastic now. The anode rod is a stiff approx 1/8th in. rod that hangs down from the nut it is secured to. The only other thing inside a gas tank is the the combination gas, thermostat valve which screws into the side of the tank. If you wish to remove the anode simply depressurize the hot water and drain a little water out of the tank and unscrew it, cut it off of the nut and screw the nut back into the hole. By removing it you will decrease the life of the tank.

                              » This message has been edited by turdchaser on 31 January 2004

                            • #295577
                              Avatar photoUTahJ


                                Thanks for the info. I think I’ll run down to the hardware store to see if they have a “bolt” that
                                will act as a temporary plug after I pull the rod out. I don’t want to destroy the rod, I just want to eliminate
                                it as a possible cause of the noise.

                                I suppose a replacement rod would have to be
                                ordered through Hotpoint, eh?

                              • #295578
                                Avatar photoDUNBAR
                                • #295579
                                  Avatar photoRetired plbg1

                                    Did you check and see if washer is loose on your CW valve going to Wh are any other valve in house including toilets.

                                    Art retired plbg

                                  • #295580
                                    Avatar photonicktheplumber

                                      I suspect that you have excessive pressure from your house water main, and that there is probably nothing wrong with your water heater. You probably tee’d off your house cold water lines from your WH cold inlet, and when a cold fixture valve shuts you are getting water hammer transmitted back to your WH. You should ahve a pressure limiting valve at the entrance of the supply line to your house. If not, intall one. As regards water hammer, you can install water hammer arrestors at each fixture, or better yet, install a multitube arrestor on the supply line where it enters the house. And, of course, make sure that all of your pipes are securely held to the structural members of your house.

                                      Finally, you could install an expansion tank atop your WH, but this helps only if your noise is due to hot water expansion, which you state you have ruled out.


                                    • #295581
                                      Avatar photobungie



                                        All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or will be taken. And yes, I am a licensed Plumber and Drainer with my own business in Brisbane Australia.

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