Total newbie here. Inherited from the local restaurant a MiniGrimac (now called the Uno, I think) which stopped working even after $350 worth of work (new seals, new solenoids etc.).

I took it completely apart and emptied about 2 lbs of mineral deposits from the innards and re-assembled. Appears to work as designed: (brew temp 203 degrees after flush, pressure capable to 12 bar, etc). The only thing that seems a little weird is that it takes an extraordinary amount of time to flush, and it only pumps about 1-1/2oz in a full minute with no portafilter on. This seems a little low to me.

I started with "French Roast" ground at the local supermarket set to "espresso" grind. Like powder.

If I use anything like 30 lbs of pressure, it takes 30-45 seconds before any liquid even comes out. I know I can tamp with less force, but would like to at least approach the "golden rule" numbers before I proceed with the learning. Everything that has come out of the thing so far has been very bitter.

So the question is: In order to minimize variables, can anyone recommend a good "starter" coffee, preferably bought from the internet (unless someone here wants to sell me a pound or two) to test with. How do I specify the grind? I know eventually if not sooner I will need to buy a grinder but right now I just want a good cup of joe.

I fear that the coffee you use is going to not fix the trouble you're having. You really are going to have to invest in a grinder. The odds of getting the correct grind when buying pre-ground coffee are similar to the odds of success at pin-the-tail-on-the-donkey played blindfolded in the dark in a hailstorm where the donkey is somewhere within a half mile of you.

HB wrote:Something is not right. Either the pump is not working correctly, or the HX is so full of scale that it's obstructed. Below is the flow rate charts for a Ulka vibration pump:

OK. Thanks for the facts. When I first got the machine, my cleanout included the "mushroom", which did indeed have a ton of crud--not scale, per se, (like calcium), but hard minerals.

I cleaned that all out and got reasonable flow (but not the levels in the chart). But before that, I pumped vinegar through the unit for several hours to descale any calcium buildup.

I suspect that from all my opening, cleaning, shaking and scrubbing, there is still stuff floating around in the system.

I do note now, that when I turn on the pump, very little flow is apparent but water is coming out the silicone drain pipe into the tray. That comes from the main brass "block" thing, which also seems to feed the HX with water.

I'm betting I still have sludge in there perhaps.

the passageways in the group might be occluded with scale and require serious descaling efforts (more than just a flush).

solenoid valves also scale up and restrict flow.


--barry "more to descaling than just the boiler"

If the gicleur valve is the little pinhole device at the top of the "mushroom", then it's clear. I think the problem may be upstream more. I removed the Head Group Screw that blocks the drill hole made in the Head Group and no water comes out there either.

Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

rfc wrote:Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

both of those can scale up, and so can the holes where the thermosyphon tubes connect to the group. and, again, the passageways in the group itself can plug up. also, check valves can stick closed.

barry wrote:

rfc wrote:Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

both of those can scale up, and so can the holes where the thermosyphon tubes connect to the group. and, again, the passageways in the group itself can plug up. also, check valves can stick closed.

I'm onto it now (I think). I have pressure all the way to the group head and I have already dis-assembled and reassembled the mushroom. I think I am down to between the orifice in the top of the mushroom (the gicleur valve?) and the holes that lead to the filter screen itself.

What does the "infusion cap" on the right side of the unit do? Just seems to be a big chamber in there?

Can the round brass thing in the center of the portafilter gasket be unscrewed without a set of snap ring spanner wrenches? I'm pretty sure that the hole beneath the group head screw is clear, which really only leaves the hole from there down to the portafilter.

Finally, I have ruled out the pressure dump solenoid, because it dumps properly when you flip the switch off.

I'm not looking to be held by the hand here, but if anyone can shed some technical light, it is much appreciated.