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  • Coffee residue from 3-way valve

    Posted by coffeegeek on February 21, 2024 at 5:38 am

    One of the three groups of our Cimbali M39 Dosatron HD suddenly started dispensing some of the ground coffee from the 3 way valve along with the water when the valve is releasing pressure after brewing. The pressure release is also much much more violent than the two other groups, causing it to splash outside the drip tray.

    Yesterday I also discovered a slight dripping of greyish/black liquid coming from the top on the outside of the group (same side as the 3 way valve). It’s covered in insulation, so I can’t directly see where it comes from (but perhaps group-split or valve). Group has an internal heating element, so top/bottom of the group is joined by a 109mm o-ring, and the 3 way has it’s usual 2 pcs 9.25mm o-rings.

    Could these 3 “problems” stem from the same fault?

    fixbear replied 2 months ago 2 Members · 3 Replies
  • 3 Replies
  • fixbear

    February 21, 2024 at 10:31 am

    That sounds like a hot puck. Upon release the sudden drop in pressure causes a collapse and part of the puck going out the exhaust. I believe that the M39 uses a mix of boiler water and cold water to reach brew temp. So you may want to look at the cold water solenoid for that head. Is the brew pressure and temp where they belong and the same as the other heads?

  • coffeegeek

    February 21, 2024 at 10:49 am

    I’ll check pressure for all three. The groups have individual temperature sensors, but all three groups show 91.5’C (cold or warm machine). And I’ve never seen them fluctuate. I always thought it was for show off. But maybe it can be enabled to show real values in the technical menu(?). Also, with another M39 Dosatron (2008) we have, it shows brew time in seconds. On this 2011, it just shows this “fake” 91.5’C all the time.

    • fixbear

      February 21, 2024 at 12:36 pm

      Remember that there are 2 cold water solenoid valves after the water meter. One feeds the heat exchanger and the other to group head above the shuttle valve(G). Also, there is a steam supply to the exhaust port (EDS) through another valve (Eds). Look at page 48 of this PDF: LaCimbali-M39TE_Tecnical_manual.pdf (

      It looks like the second cold water is to make sure the exhaust shuttle seats as well as blend.

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