CH expansion vessel

Discussion in 'Plumbers' Talk' started by ron, Sep 19, 2004.

  1. ron

    ron Guest

    My expansion tank has either failed or is not big enough (pressure>3bar when hot, zero when cold etc.). I have a Worcester heatslave 20/25 which can apparently cope with up to 180 litres before adding more exp vessels. I have 15 radiators (doubles 600x520) which I have assumed are about 4 litres each (but have no real idea). Pipework volume (45m 22mm, 40m 10mm) is about 20 litres and the boiler is stated at 71 litres. I make that ok at 151 litres.

    Have I underestimated the volume (particularly the rads) or is my expansion tank knackered? There is only air coming out of the tyre valve thing... no water. Definately no pipe leaks as pressure holds when not heating.

    Also... one thing that does confuse me is why the pressure in the expansion vessel remains at about 0.7 bar even when the system hits 3! I'd have though it would've increased a measureable amount if not to 3bar!

    Long post... sorry. Thanks for any advice!
     
  2. Plumbbib

    Plumbbib New Member

    Is your PRV blowing off??
    Is there air in your exp. vessel?
     
  3. stolenink

    stolenink New Member

    This is an interesting subject. Initially, is there a valve betewwn the system and the expansion vessel? the vessel pressure will increase with the system warming up. Another worry for me is that the 'cold fill' pressure is zero. You should have at least 1 bar in the system at all times. A 3 bar pressure rise would also indicate that the expansion vessel is either isolated or devoid of air or burst bladder. The system water content working roughly on 12 litres per kW is (based on the output of the 20/25) is 300 litres.

    Follow this link http://tinyurl.com/4jz4v

    It helps with the selection of the vessel. Don't forget to include the internal vessel size.

    Check these out and keep us informed.
     
  4. Queeg

    Queeg New Member

    If you have 2 different pressures like that, I'd bet it's a blocked hose linking your expansion vessel to the boiler.

    The solution: Isolate the system and release the pressure or if you can't do this, drain it down. Then get a big towel ready and hold it around the braided hose pipe connection adjacent to the boiler (not the EV end) while you unbolt it. That should be OK and not leak too much. Repeat with the other end of the pipe. If it's blocked, you will have one heck of a spray of filthy water coming out of your expansion vessel while it equalises. Take the pipe off completely and either replace (ideally) or clean it out with a small rod being careful not to damage it.

    Once you've reassembled it, really flush the system and then top it up with the right inhibitor. The flushing is seriously important as the problem probably arose by poor flushing at the outset - quite common with microbore.

    Hope that helps, let us know how you get on.

    Queeg.
     

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