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San Marino Lisa - group head losing prime?

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  • San Marino Lisa - group head losing prime?

    We have purchased a 2nd hand San Marino Lisa 2-group machine (the variety with a manual pour switch and no others). We have it fitted in our mobile trailer and has been a great machine for our purposes. But, one cold and frosty morn, the machine worked well for the first pour of the morning but then if I let it sit for more than a minute or so without using either group-head, the machine would lose prime. The only way I could stop it from losing prime was to run the group head every thirty seconds or so and if I failed to do so then I would have to turn the whole machine off for 4-5minutes and then switch it back on and it would reprime itself. All that time, the steam wand and hot water is working fine. We pump water out of 10 litre spring-water bottles and the hot water is running back into these and heating them up. The pump pressure gauge now resides in the green area wether the machine is on or off and max's out when pouring a shot (when able). It seems to me like an air leak somewhere allowing it to lose prime, but I don't know where to start looking. Any help would be appreciated

  • #2
    There would be many other, more equiped then myself to offer any sort of constructive advice however,I have a single group heat exchanger (Bezzera) machine set up in our staff room at my work,it works beautifully and unlike your unfortunate situation,ours has not (touch wood!) shown any indication of potential difficulties.
    Our unit is simply directly connected ,via external rotary pump (energised via bezzera controls) to a Bunnings "cheap"$8.00 PVC non return valve,to a twenty litre water vessel (Plastic bucket).
    I have an accumulator tank (non pressureised) available to counter any possible pump suction hesitation,haven't needed it.
    Waste is collected via the standard drip tray collection outlet to a small waste container.
    Is your's similar? I'm interested how your's directs hot water back into the water storage,most odd!
    The water level probe may need replacing or at least a good scrub/clean.
    Some pictures would be helpful.
    Last edited by mulquemi; 31 July 2015, 10:37 PM. Reason: One more thing!


    • #3
      Originally posted by ErinMor View Post
      We pump water out of 10 litre spring-water bottles and the hot water is running back into these and heating them up.
      This sounds like the one-way valve built into the expansion valve is allowing hot water to escape from the heat exchangers back into the the water supply. Or possibly the fill solenoid to the boiler is allowing hot water to seep back out of the boiler - I have had this happen before on a machine. Since on a plumbed machine the pressure into the fill solenoid is always higher than the pressure in the boiler (and the fill solenoid resists seepage when closed better in one direction than the other) I fixed it by reversing the body of the solenoid (swapping inlet and outlet).

      This is the expansion valve, you'll find it under the drip tray with a pipe leading from the outlet on the left of the pic into the drain bowl. At the bottom of the valve a fitting screws on with a filter inside, this is to the right hand side of the machine as the valve sits in the machine. If you disconnected this fitting from the water manifold to the right of it and let the machine sit for a while with the boiler heated up, you'll be able to tell if the hot water is coming from here (failed expansion valve) or if it is coming from the boiler.
      And the best idea when running a machine from a bottle is to fit a non-return valve to the end of the hose dunked into the bottle, to stop air getting into the hose when swapping bottles.


      • #4
        Thank you both for your replies. Our machine has no expansion valves under the drip tray at the junction pictured but I followed the feed line toward the boiler and found a 1-way valve which I removed. This had a small amount of rubbish in it, which I removed, and then blew through it against the direction of flow to find that it isn't sealing. I also ran water through it backwards with the same result, so I am concluding that I have a failed 1-way valve. (which has allowed water to flow back from the boiler to the water source, heating it up, and allowed the machine to lose prime). I've ordered one from coffee parts and I will also fit a non return valve to the end of the feed hose, as suggested. I'll let you know how I get on. Thanks you both again


        • #5
          So far I have replaced the one way valve and since then the macine has not lost prime and I have had no more hot water coming back down the feed line. I also noticed that water was leaking from the solenoid at the moment I turned the group head off so I checked the o-ring and replaced it which sees to have fixed that problem. But now I have little to no pressure coming thru the left group head - I have cleaned the shower screen and checked the piping from the boiler to where it screws into the group head outlet, which all looks fine so could this be a blockage or is there some other explaination for it? My pump gauge on the machine has also set its zero (reading when the machine is off) in the red and then the dial bumps into the boiler pressure gauge when it is pumping - is there an easy fix for that?


          • #6
            Hi, it sounds like you may be chasing scale or debris. The left group gicleur (jet; orfice ) may have scale obstructing flow from the thermosyphon circuit. This requires opening the top of the left group and ensuring the jet is clear. The diameter is very, very small and it doesn't take much to block it.


            • #7
              Addendum: there's a steel mesh filter surrounding the jet. This may be clogged with scale as well. It can be soaked in a descale solution and reused.