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Discuss Cold water leaking through tundish after service of cylinder in the Central Heating Forum area at

  1. proppi

    proppi New Member


    We have had our unvented cylinder serviced for the first time a few days ago (the whole heating system is brand new, well one year old :)).

    Soon after the service I noticed cold water dripping through the tundish. The company who did the service sent another engineer who said the pressure reducing valve on the cold water inlet was letting by and suggested replacement.

    I am a bit surprised about the suggestion that the PRV is faulty, firstly because the system is almost new and secondly because everything worked fine until the service was done.

    So before I agree to have the PRV replaced for a lot of money (only to maybe discover later that this was not the source of the problem) I wanted to get the view of the experts here. Does this make sense or is it more likely that something was done wrongly in the service that is much easier to correct (eg expansion vessel wrongly pressurised).

    Thanks a lot for your help!
  2. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    If it has been serviced by a qualified and experienced individual, he/she will have or should have tested PRV and T&PRV.

    Due to design, they will often not seat back down correctly after being opened for the first time in months or years.

    This is not the fault of the Engineer. If anything, to me it suggests they did their job properly.

    It may settle after a day or two but I doubt it.

    It is possible that it is an incorrect pressure in the expansion vessel but to test that theory, if you open a hot water tap, once the increase in pressure has been released the PRV would stop dripping, even if only for a short while.

    There are other things that might cause a PRV to pass/operate but the person who serviced it will have checked for those things I would think/hope.

    The vessel pressure and Governor pressure would have been checked during the service.
    • Agree Agree x 3
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    Last edited: Apr 26, 2018
  3. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    Couldn’t have put it better myself lol
    I serviced one a few weeks ago that hadnt ever been done before TPRvalve would not reseat . Not my fault, not the customers fault , its just what happens.
    • Like Like x 1
    • Agree Agree x 1
  4. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    As above it can happen and quite often does . kop
    • Like Like x 1
  5. AWheating

    AWheating Trusted Plumber GSR

    As above, sounds like the engineer did the correct tests and the valve has not reseated. It happens a lot.
    • Like Like x 2
  6. proppi

    proppi New Member

    Many thanks Last Plumber for an excellent explanation and many thanks to all the others too.

    Looks like I will have to bite the bullet and get a new PRV installed. I just hope that not all future services are going to end so troublesome, otherwise maintenance of the cylinder is going to cost me a fortune.
    • Like Like x 2
  7. YorkshireDave

    YorkshireDave Plumber Top Contributor!!

    Personally, when they do that I strip 'em down and clean the seat. Works 50% of the time and only takes a few minutes. Possibly worth a go...?
    • Agree Agree x 1
  8. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    I normally include the cost of the new prvs in the service
    • Agree Agree x 1
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