Water Boiler Growl/Pressure Release Sound

Hi All,

I've noticed fairly recently that I hear a sound from my gas hot water boiler every now and then that sounds like a short his/pressure release/growl. The sound usually lasts 1 to 2 seconds, I'm wondering if this is normal or needs to be checked.

I have noticed that there is a Non Return Isolating valve which seems to be half open half closed, should this be left as is or should it be open or closed?



  • There's a pressure relief valve at the top of the tank that will automatically open and shut when required. That's probably the noise you are hearing and usually normal.

    It's recommended that the valve is manually opened and closed every few months to ensure that it's working correctly.

    A little hot water and steam should come out.

    • Great thank you, does that mean the Non Return Isolating valve should usually be in the closed position but opened preiodically?

      • +1

        The non-return valve is different to the over-pressure safety valve.

        The non-return is to prevent water from the boiler from flowing back into (and contaminating) the incoming cold water main.
        Stored hot water can be a haven for thermo-tolerant bacteria.
        This shouldn't be fiddled with at all IFAIK.

        The over-pressure valve is to prevent your Hot water service from turning into a steam powered bomb.
        Probably good practice to ensure this is venting correctly and not clogged with dirt/dust/scale.

        • Thanks, I think this is the case, I closed the valve and noticed the hot water pressure dropped, so it seems like it's the cold water inlet with the non return like you mentioned. returned it to open as it was and decided I shouldn't mess with things I don't understand

  • That's correct, normally closed, a quick 'squirt' is needed every now and again to ensure that it's operating correctly.

    • +1

      I take long showers for that

  • Maybe it is angry with you

  • OP, how old is your hot water boiler? If more than 10 years that’s when it can start having problems… YMMV.

    • it was here when I bought the house but I believe it was replaced not long before that so just a few years.

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