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Discuss Screaming hot water pipes after PRV fitted! in the Plumbing Forum area at

  1. Mike beaumont

    Mike beaumont New Member

    Hi all, I've fitted a PRV due to problems I've recently learnt. Long story short- I have high pressure and low flow, pressure being 10 bar and restricted flow by either crushed pipe or age related debris build up ( my home was built in 1954). Due to finances I can't afford a new water main coming in so to save the appliances of the new incoming kitchen I've put a PRV in and set it to 4 bar, all of a sudden the hot water feed from various taps start a huge high pitched scream almost when it sarts to flow hot! Terrible noise that's scaring the kids any advice welcome!!
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Is it just the hot ? Not the cold etc

    What system do you have cylinder, combi etc
  3. Chuck

    Chuck Active Member

    If you have an unvented hot water system, get whoever services it to check it.

    Otherwise, get the incoming main repaired and have the water company reset the supply pressure to a more normal value (3-5bar). Then remove your PRV.

    I'm surprised they agreed to increase it to 10 bar in the first place. How long has it been like that?
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Sometimes they don't lower the pressure as there's other factors like where's the pumping station etc
  5. Mike beaumont

    Mike beaumont New Member

    Open vented cylinder system, oil fired, only on the hot.
  6. Mike beaumont

    Mike beaumont New Member

    There's 10 bar on the mains outside my property to feed the farms up the hill, I'm connected to that. Welsh water are happy to cover the cost of PRV, so as far as since I've been there, there's 10 bar at the taps but the flow slows right down, always has done. It's all only come to light after I've been replacing taps washers left, right and center and a few other things over the years that I finally investigated the problem. I thought the PRV will save the appliances for a while but I didn't want to incur further problems! Tempted to take it off again!
  7. Chuck

    Chuck Active Member

    Most likely suspect based on your description is a form of 'water hammer' associated with the float valve controling the level in the feed tank for the HW cyclinder. The problem with water hammer is that is often a combination of two factors that cause it.

    In order of hassle try:

    1. New washer in float valve
    2. Replace float valve with good quality with pressure spec in the correct range.
    3. Make sure pipework is securely clipped at the correct intervals (1.25 m max between clips).
  8. Chuck

    Chuck Active Member

    Oh, okay, rural supply :(

    If the problem is with your external pipework I'd advise fixing it before it fails completely. If your flow is already 'slow' you are not far from 'none' and a house with no water supply is very unpleasant to try to live in. (If you have kids or are married you really don't want to find out the hard way...)

    Have WW confirmed that the flow rate amd dynamic pressure are up to spec at the point the main crosses your boundary? If not you should be able to get them to make improvements.

    You can cut costs by digging the trench yourself. A digger and driver are a couple of hundred quid per day and they can do a lot of work in a day. Another option that makes less mess is a firm that specialises in water-pipe renewal using 'impact moling' that avoids conventional digging.
  9. Mike beaumont

    Mike beaumont New Member

    Ok I can check this out. UPDATE. The IS coming from the PRV when the water starts to flow hot. I've turned the PRV down to take 2bar, this has dramatically reduced the noise and duration of it but it still goes. I'm reluctant to turn it down further as we do need a bit of pressure for the shower etc and wondering why the PRV is making the noise ( which is obvious - the wife spotted it yesterday morning and confirmed by myself last night!) Is this a common problem for PRV's or can it be something with the hot water cylinder or the feed to the expansion tank in the attic? Thanks all for advice so far!!
  10. Mike beaumont

    Mike beaumont New Member

    The pressure has been confirmed by Welsh Water and the flow (although not checked for rate of flow) assessed by a professional plumber.
  11. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Any chance of a pic of the prv ?
  12. Mike beaumont

    Mike beaumont New Member

    Will take one tonight.
  13. Chuck

    Chuck Active Member

    So, it seems to be the case that the noise starts when the header tank starts to fill, which will be a short time, say 20s, after you start running hot water.

    Debris in a PRV can cause a squealing noise.

    I think, however, that this could all track back to your low flow issue. I suspect that if you measure the dynamic pressure at the inlet to the PRV you will find that it drops down when the header tank starts filling to the point where the pressure drop across the PRV is not sufficient for it to operate correctly. That's why reducing the PRV output, which increases the operating differential, helps.

    Replacing the cone in the float valve with a more restrictive one might stop the screaming, but your tank will fill more slowly, which will cause other issues. It's possible that an accumulator would help, but IMO you need to get the flow rate and dynamic pressure measured at the property boundary and at the stopcock inside the house before making any decisions.
  14. Gasinspect

    Gasinspect Member

    Had this once where flow was poor, it was a small pebble in the pipe that rose under pressure to a narrow point in pipes, then fell back when taps turned off. Cured by undoing pipe at stop valve and back flushing pipe, stone popped out and problem solved.
    • Like Like x 1
  15. justlead1

    justlead1 Trusted Plumber GSR

    The mechanics of the PRV simply reduce the flow (Smaller area) as such it can behave like a whistle. 10 bar down to a working pressure is a great reduction in one go. Two in line may be a answer as this will take it down in stages. (10 to 6 then 6 to 3) perhaps. If the supply problems are corrosion opt for planned maintenance and renew, as when a burst occurs it costs a lot more on with the hurry up approach.
    Good Luck
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