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Thread: La Cimbali Junior M21 S / Fault leaking steam + boiler refilling

  1. #1
    Senior Member
    Join Date
    Oct 2015

    La Cimbali Junior M21 S / Fault leaking steam + boiler refilling

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi All,

    I have picked up used La Cimbali M21 Junior S (this is the non-automatic tank model). Machine history 2002 model, purchased second hand and was most recently used in a coffee cart, has sat unused for a period of few years. It has a fault with steam venting from the top of the boiler and continually refilling the boiler every few minutes.

    In terms of my experience, very limited on commercial machines, I have replaced group seals and steam valves on a few machines. I have a Gaggia Classic as my daily driver, I have used a couple of HX machines.

    Here is what happens when powered on;
    1. Yellow LED starts blinking
    2. Boiler auto fills takes 10 seconds then stops auto-filling
    3. After a minute or two steam starts (quite dry) coming out of the boiler vertically from a valve
    4. The pressure gauge never seems to get anywhere near green zone and doesn't really seem to move
    8. But the machine never builds pressure (at least according to the gauge) and will not reach temperature

    Couple of notes (while powered on);
    - If I open the steam wand get some pretty wet steam
    - The hot water function works with water running but I can touch it and not super hot
    - If I press the coffee button it runs water through the group until stopped

    Pic of part venting steam on top of boiler;

    Questions I have;
    1. Just wondering what peoples thoughts are on fault? I am thinking faulty pressure stat but would welcome advice
    2. The valve on the boiler which is venting steam, is that Anti Vac Valve, Safety Valve?

    Last edited by roosterben; 17th July 2018 at 10:18 AM. Reason: Add picture

  2. #2
    Super Moderator Javaphile's Avatar
    Join Date
    Dec 2004
    It looks to be the anti-vac valve and it's stuck open. Clean and replace the o-ring in it and the washer it seals to the tank with or replace it and you should be good to go. At least as far as this problem goes.

    Java "Pssssssst" phile
    Toys! I must have new toys!!!

  3. #3
    Senior Member
    Join Date
    Oct 2015
    Thanks Javaphile will give that a go, I will update the post, hopefully tomorrow night I get some time to tinker.

  4. #4
    Senior Member
    Join Date
    Oct 2015
    Well happy with that, thanks again Javaphile, machine is working pretty well!

    I did a quick check of the pressure gauge and removed the lines, clean as a whistle, no sign of scale, gave it a bit of air pressure and the needle moved.

    Then I found a socket which fit the anti vac valve, removed the plastic parts and they seemed in good condition, the o-ring was still flexible and I don't have any replacement ones handy so I put it back in. Tightened the nut up and fired up the machine.

    Voila! It did one little spurt out the anti vac valve while heating and built up to pressure about 0.8 bar in the green zone.

    I tested the steam, hot water and made a really crappy double shot (grinder is dialed in for the Gaggia and the M21 needs a finer grind I think) just to test and all seems to be working nicely.

    One other thing is the drip tray has a hole and came with a drain pipe and o-ring, this ends up leaking as I am not using the drain so will find something to plug it with that is removable.

    Next steps to are;

    1. Check the group seal and shower basket and see what sort of shape they are in
    2. Descale the machine
    3. Do a salt treatment on the water filter

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