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Vaillant Turbomax 242 losing pressure

Discussion in 'Plumbing and Central Heating' started by primetime, 30 Oct 2019.

  1. primetime


    20 May 2013
    Thanks Received:
    United Kingdom

    Turbomax is losing pressure and needs topping up a couple of times a day.

    What I've checked
    - No leaks in all the pipework I can easily get to. No marks on ceilings etc.
    - Isolated CH flow and return at boiler and pressure still drops.
    - PRV is not venting, have never seen the pressure anywhere near 3bar in operation.
    - Expansion tank did expel some water when the valve was depressed.
    - Re-charging the expansion tank also increases system pressure.
    - The AAV looks like it has had water escape from it at some point but probably some while ago.
    - All rads coming up to temperature and have been vented of air. System refilled afterwards.

    I'm guessing the expansion vessel is at fault but don't understand where the pressure is constantly being lost with no leaks and no activation of the PRV. Could it be something internal? How could I check for this?

    Moving ahead...
    The boiler is old and could do with replacing but wanted to hold off until Spring. Rather than replace the installed expansion vessel I'd look to add one on the CH return near the boiler but given the symptoms above, not sure how much good this would do.

    Also looking for size recommendations for a replacement boiler. I'd need to go a bit higher than the current 24kW as there has been an additional 4 radiators added since the Vaillant was installed. Also an extra shower but both showers wouldn't normally run at the same time.


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