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Grimac mia- loss of boiler pressure

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  • Grimac mia- loss of boiler pressure

    Hi there I am new to this site and have recently purchased a Grimac Mia. I am very happy with the machine and internals and boiler look in great condition for a used machine. The only issue I have is it fails to maintain boiler pressure. When it heats up and reaches pressure and heating element switches off I notice a slow pressure drop as confirmed on the gauge which occurs at idle. As the pressure drops the heating element switches on to maintain pressure. I understand this would occur when steaming but when at idle I thought it should hold pressure. Cant seem to locate any leaks and the pressure relief valve has been replaced. The anti-vacuum valve appears to be working ok but not sure if it has been replaced. Does anyone have any ideas? I have seen some of these machines refurbished where all connections to the boiler have been thread taped would this be a good start to help isolate the problem? Machine has been descaled and apart from this issue works great. Any advice would be appreciated. Cheers Mick

  • #2
    That's normal behaviour for this and other pressurestat controlled machines. The pressure drops as the water cools in the boiler then the pressurestat kicks back in to switch on the element and bring the pressure up.

    How far on the gauge does the needle swing in this switching cycle? If it is too far then the pressurestat deadband (point between switch off and switch on) may be too big. This is a problem and the pressurestat would need to be replaced.


    • #3
      Thanks for the reply. The pressure gauge drops to around 1.3 bar from 1.5 bar and the element switchs on and the pressure rises again. I understand that as the water cools the need to switch element on to maintain pressure but it appears the pressure is dropping at a fast rate. Once it reaches pressure it drops pressure within 15-20 sec. And the element kicks in. And this continues. I was concerned of a leak somewhere in the boiler?


      • #4
        All normal,

        Cycling rate will be determined by element capacity and thermal characteristics of the boiler. If it had a leak, you'd either hear steam or get a progressive overfill.


        • #5
          Yeah, this is normal behavior. I have a BFC classica, which i think are re-badged Grimac's or the other way around. Heater elements turn on, water boils, pressure is increased. Once pressure is reached, heating elements are turned off. Once pressure reaches a certain point, elements are turned back on again and the process is repeated.

          As these machines are heat exchanges i don't believe the pressure drop is going to affect your brew in any sort of way.

          Steaming doesn't seem to be affected as well(not that i can visibly tell) although one could in theory say that you are not getting the same amount of pressure when the elements are off as opposed to on.


          • #6
            I had a Grimac La Uno (same internals), and what you are describing seems to be about right.
            You'll find that boiler setting is quite high. I used to run mine between 1.1 and 1.2.

            Do you have a thermo siphon restrictor fitted? Up to you, but it’s worth it.
            You’ll be scorching your coffee at that temp without one.
            That's part of the reason the element kicks in so often, because the boiler temp is quite high.

            The only way to slow the losses is to install some boiler insulation.
            Otherwise it’s a great machine, easy to work on, huge water tank and should last years.
            A friend of mine had one for 17 years before it had a brain box failure about a week ago.
            Instead of fixing it he traded it in on a new machine.


            • #7
              Thanks to all who have replied much appreciated. I was concerned that there was a problem with the element kicking in so often and seeing that pressure gauge drop when at idle so quick. Just wondering what a thermo siphon restrictor is? Dont think my machine has one. What does it do. Does it reduce the boiler pressure? Will adjusting the pressure stat help reduce temperature. Cheers


              • #8
                Hi everyone well have found the issue I think. Upon starting up the machine have noticed upon building pressure a small amount of water seeping from around the fitting on the boiler that supplies water to the group head. Not sure if this had a gasket type seal thats worn out. I have seen some photos of this boiler where there appears to a white sealing compound where the fitting enters the boiler. Any ideas to fix locktite or treadtape? Cheers😀


                • #9
                  A product made by Loxeal "Thread Sealant 58-11" is great for this sort of work. Bunnings usually keep it in stock.
                  Have been using it for a number of years and it has never let me down yet plus, it's safe for use with Potable Water.
                  Here's a PDF document from the manufacturer...



                  • #10
                    Thanks Mal have used this product and awaiting for it to cure. Will test out tomorrow and see how things go. Cheers