Hot Water Pipe Noise

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    • #279816
      Bob Oshiro

      We have an instantaneous/continuous outside water heater. The sound of constant running water can be heard from all taps in the house but none have any leaks. When tap supplying water to heater is turned off, noise stops and meter shows no usage. When this tap is on, meter does show usage even though all internals taps off. Mains water supply to house shows no sign of leakage noise so we can assume that it is isolated to the hot water supply only. With water supply to heater turned off noise (like a hissing/escaping sound) can still be heard from taps even though no water is passing through. There is no release valve on the outside of the heater to relieve any pressure so we do not know whether there should be one on this type of heater.We have tried turning all hot taps on and letting the water run for a period of time to see if this will stop and it doesn’t. Can anyone give us an ideas to what this might be please?

    • #301731
      Retired plbg1

      Sounds like you have too much water press. C heck it out

      Art retired plbg

    • #301732

      Thanks for the reply Art. Where would we be able to lower the pressure at the water heater? I can’t find any labeled adjustment. The overall pressure could be lowered at the mains by the road but the ideal would be for the hot water only. Any thoughts?

    • #301735

      Are you certain the noise you are hearing is not the Fan motor running in the water heater after the heater has been used – they can run for up to 7 minutes after use.

      If you turn off the valve feeding the cold water into the water heater and the noise stops and turning it on again starts the hissing noise then I am sorry to say but there is a water leak somewhere in your piping system albeit a very small one.

    • #301736

      Sorry I should have added that your water leak will be on a hot water line or fitting not a cold one becuase when you shut the valve under the water heater ( cold line into unit ) you are effectively shutting down the hot water outlet to all fittings, cold water faucets etc would still operate when this tap/valve is shut. Hope this helps.

    • #301737

      Thank you for the reply Selgas. I appreciate your comments and will investigate the possibility of a leak somewhere in the hot water pipes after exploring any other options. The thing we find which seems so strange though is that with the water intake turned off to the heater isolating the hot water pipes, noise (sounds like air escaping and not really a hissing sound as mentioned earlier) can still be heard when you turn on a tap even though no water is passing. If a leak is in these pipes somewhere how are we able to hear this noise when no pressure is present ?

    • #301738

      Obviously if you shut down the water supply into your water heater the interior pipework and fittings will still be under pressure and if a leak does exist within your hot water system then a noise could still be heard until the pressure drops away to nothing then all should become silent.

      You have not said if your water heater is an electronic one that has an electric fan for combustion in it – if it has then the noise may be the fan motor which should still remain running for up to 7 minutes after the water heater has shut down. These do in time run bearings in the motors and can give a sound similar to your description when they are operating. Let me know huh.

    • #301739

      Hi Selgas,

      The heater is a “Vulcan Continuous Gas Water Heater” and does not have an electric fan. I have left the taps in the open position for quite some time with the water turned off to the heater and still the noise is there. As you said, the pressure would drop away to nothing after a period of time but in this case it does not unfortunately.I am keeping my fingers crossed that if it is a leak it is not underneath the concrete slab of the house as this would no doubt be a disaster.

           I am extremely grateful for your help and look forward to your comments.


    • #301744

      The heater you have there is a Vulcan – can I take it that you are in Australia then?? If so the water heater you have is a mains pressure storage tank – not an instantaneous water heater as first muted. If it is a Vulcan storage tank the hissing you can hear may in fact be coming from a leaking TPR valve on the side of the cylinder – here in NZ we have one on the cold water into the heater and one on the hot side usually on a seperate connection. Turn on the mains water valve allow the heater to settle shut all the hot water taps off and after 15 minutes or so go check the valve on the top of the water heater if it letting water continually flow then it needs replacing, if it only lets water flow for a very short time directly after the main burner has lit up and until it shuts down again it is doing it’s job – that is allowing for the expansion of hot water and the added build up of pressure to be released. It should not allow water to flow continually – it needs replacing if that is the case.

    • #301786

      The two most common causes for such noises are steam and sediment in the tank. You can often correct steam problems by merely lowering the thermostat setting. Or …………

      Run the hot water in the tub or shower until you get all the air out of the line.

      The reason you get air in the pipe could be caused by the water department . They could have repaired a water main; and air got in the line. Check with the city water dept. to see if that may be the case.

      If you’re on well water, the water table may be low and the pump is picking up air and sending it into your house. Try running your garden hose to get all the air out. DUNBAR2007-12-21 16:08:35

    • #301787


      If you have got “Steam” in the cylinder I think you will find that the problem is a hell of a lot more than what you have suggested – there is NO WAY steam should be able to accumulate in a mains pressure storage water heater when it has a TPR Valve fitted to it which will blow full open and discharge the hot water as well as relasing the pressure when the hot water at the top of the tank reaches 98 dgrees C – which is of course 2 degrees below boiling point.

      I also beleive you will find that the person asking the questions is based in Australia going from the brand of the water tank they have stated in their posting and our rules for Mains Pressure systems are a little different to those in the great US of A.

    • #301788

      Have you ever turned off one of your faucets only to experience a loud noise accompanied by vibrations? If so, you experienced “water hammering” and had yourself a case of noisy water pipes. Water hammering is caused when a fast-moving stream of water travels down a narrow pipe and suddenly comes to a closed valve where it must come to an unexpected halt. It can be fixed.

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