Why does the pressure gauge on a combi boiler keep going down?

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  • Why does the pressure gauge on a combi boiler keep going down?

    In one of my properties the pressure gauge keeps dropping low. Why is that?

  • #2
    Water leaking?
    JEFFREY SHAW, solicitor [and Topic Expert], Nether Edge Law*
    1. Public advice is believed accurate, but I accept no legal responsibility except to direct-paying private clients.
    2. Telephone advice: see http://www.landlordzone.co.uk/forums/showthread.php?t=34638.
    3. For paid advice about conveyancing/leaseholds/L&T, contact me* and become a private client.
    4. *- Contact info: click on my name (blue-highlight link).

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    • #3
      When I inherited mine, I was told to keep topping it up. This takes the pressure up to maybe 1.5 atm. This usually sinks to 1 over the next fortnight, but stays there. I have not topped mine up for maybe a year, and it is still at 1. What does yours go down to?

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      • #4
        How old is the combi? Is it an old system with a separate tank to supply pressurised air? If it is a new combi then you proably have a leak somewhere.

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        • #5
          Originally posted by SMurray View Post
          In one of my properties the pressure gauge keeps dropping low. Why is that?
          Can be a leak, but another highly likely cause, if it's fairly old, is that the expansion vessel in the boiler is stuffed. If so you'll be getting water coming out of the pressure relief valve (outside - it's a good idea to hang a carrier bag over it to see if it catches any water when you aren't there.

          Here's a useful guide which explains all about it.

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          • #6
            Originally posted by jamesknight0 View Post
            When I inherited mine, I was told to keep topping it up. This takes the pressure up to maybe 1.5 atm. This usually sinks to 1 over the next fortnight, but stays there. I have not topped mine up for maybe a year, and it is still at 1.
            Ours is labelled that pressure should be kept between 1.0 and 2.5. There's also:
            a. a warning to call the Service Engineer if it drops below 0.5 or rises above 2.5; and
            b. a small blue tap that enables us to add more water if/when it drops towards the minimum.
            JEFFREY SHAW, solicitor [and Topic Expert], Nether Edge Law*
            1. Public advice is believed accurate, but I accept no legal responsibility except to direct-paying private clients.
            2. Telephone advice: see http://www.landlordzone.co.uk/forums/showthread.php?t=34638.
            3. For paid advice about conveyancing/leaseholds/L&T, contact me* and become a private client.
            4. *- Contact info: click on my name (blue-highlight link).

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            • #7
              Its not that old - 4 years, worchester combi. I can't see any water leaks...

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              • #8
                Its a worchester combi about 4-5 years old. I cant see any leaks.

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                • #9
                  Originally posted by SMurray View Post
                  Its a worchester combi about 4-5 years old. I cant see any leaks.
                  You're unlikely to do so if it's the expansion vessel that's gone... did you try the carrier bag trick?

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                  • #10
                    Ericthelobster is right - it is most likely the expansion vessel. had the exact same problem and this week had a heating engineer out to sort it - not too pricey at all - about £150 all told. as ericthelobster has said, you need to find the pressure relief pipe - it will be a run of copper pipe from the boiler to outside somewhere - probably will end above a drain. When I found there was a problem a few weeks back, I put an old paint tray under the relief/overflow pipe, put the heating on full blast (to max the pressure) and 20 minutes later had a tray full of hot water.

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                    • #11
                      Hey thanks for all this. What's the carrier bag trick?

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                      • #12
                        Originally posted by SMurray View Post
                        Hey thanks for all this. What's the carrier bag trick?
                        Well, not exactly a "trick" - I was just referring you back to my post #5 in this thread!

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