Hi Folks! My Astra PRO acts very finicky at times when I try to pull a shot and I can't quite figure it out. When I flip the brew switch, the ULKA (EAX5) pump will emit a humming noise rather than the noise you'd expect to hear when properly pumping (and no water comes out at the group head). I have replaced the pump a couple of times expecting that to fix it (..as there are a lot of threads out there on ULKA's humming and many times this is the fix), but just this morning, it started humming again - and I replaced it just yesterday .

In this particular case, it almost seems like something electrical is not firing (maybe a relay?), because if I give the front of the machine a nice firm pop with my hand, I will hear the clicking sound of a relay(?) and the pump will engage and pull a shot fine. Note that I am not tapping the pump itself and do not believe this could be the stuck ball within the pump issue (which I've also read about).

As for some history, it's kinda hit or miss on whether or not the pump will run. It has done fine for months at a time only to start acting up randomly. Sometimes the 'ol smack on the front works and sometimes I cannot get it to pump no matter what I try. I've disassembled each pump and see no scale or anything physically wrong. And most of these pumps that I've removed and torn down will run again - at least for a bit - when I reinstall them. I have a feeling the pump is not my issue (although this is a pourover machine and the reservoir water does get up to about 90*F after the machine has been on for a while, which is above the input water max temp spec for these ULKA's - so that could be slowly killing the pumps).

The Fluid-O-Tech vibe pumps are rated for much higher temp input water and I wouldn't mind converting to one of those, but if there is an electrical issue or some other non-pump issue, it sounds like it might be a frustrating waste of money.

Maybe I have a couple variables going on here? I appreciate any thoughts from the community as I am at a loss and really do not want to toss this machine. It is absolutely excellent when it works!

Thanks in advance!

-Chris

If the pump is getting mains voltage and stalling at less than 10 Bar, then the pump is no good.

Usually, if the pump is stalling the pump is dying, but if you can measure pressure (or approximate a measurement like with your thumb over the steam wand in a SBDU) then you have better evidence ie. "My thumb is stronger than the pump, the pump is dead".

On the pumps that no longer work, you checked mechanically and found no fault. Did you check electrically? If not, use your multimeter in ohms position and read the terminal resistance, then do it again with probes reversed. If you get no reading either way, then either the coil or the internal diode is failed open. If you get a reading, but it's the same reading in both directions, then the coil is okay, but the internal diode is failed shorted. Pumps with the internal diode failed open won't hum at all. Those with the diode failed shorted will hum but not pump, although when hooked to a water source without restriction (i.e., removed from the machine), a trickle may flow, but they won't develop pressure.

I have three EAX5's (120V 60Hz 52W) - two of them have been used in the Astra and one is brand new. If I set my multimeter to ohms (Ω) and take a measurement, I get:

Pump 1 (used): 52.8 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0.L on multimeter display) when reversed
Pump 2 (used): 69.7 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0.L on multimeter display) when reversed
Pump 3 (new): 59.4 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0.L on multimeter display) when reversed

What might this indicate? The behavior is the same between all three pumps, but the readings vary a bit.

One thing on my list to do is reproduce the issue and take voltage readings at the pump when it's humming. I would like to try and determine why I can smack the front of the machine with my hand sometimes and get the pump going again...hearing something like a relay engage or disengage when I smack it...if that makes sense.

Thanks!

Those reading don't make much sense as they indicate those would be only 2 or 3 watt pumps. Since the diode is internal, your meter is measuring the diode as a resistor and that's undefined. My Fluke shows diodes having a resistance of about 1.5Meg ohms and my $4 Harbor Freight meter shows different resistances for different ranges. Since meters effectively measure resistance as the voltage drop across the test resistance and diodes add a fixed drop of something around .4 to .9 volts, you can't get there from here.

I changed some range settings on my multimeter (I am not good with these things outside of measuring voltages, really - but trying to learn) and got the following:

Pump 1 (used): 214.2 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0L. on multimeter display) when reversed
Pump 2 (used): 281.2 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0L. on multimeter display) when reversed
Pump 3 (new): 237.0 kΩ (red probe on terminal that aligns with the diode marker) - no reading (0L. on multimeter display) when reversed

Thanks!

Switching to MΩ on my multimeter gets me:

Pump 1 (used): 1.056 MΩ (red probe on terminal that aligns with the diode marker) - no reading (.0L on multimeter display) when reversed
Pump 2 (used): 1.356 MΩ (red probe on terminal that aligns with the diode marker) - no reading (.0L on multimeter display) when reversed
Pump 3 (new): 1.167 MΩ (red probe on terminal that aligns with the diode marker) - no reading (.0L on multimeter display) when reversed

As I said, it's meaningless other than telling you that the diode is working. the resistance of the coil is more likely in the range of 50-250 ohms and unless you can get the diode out of the circuit, there is noting more you can tell.

10-4. So there is a chance that all of these pumps are good and something is not always letting the right amount of power get to the pumps to do their job? I guess getting a voltage reading while the issue is occurring is where I should look next. Maybe Astra will also provide me with an electrical schematic for the machine too. I will report back when I get some voltage readings. Thanks!

Yes, your pumps all appear to be electrically fine. As Ira says, you can't imply much from the readings beyond the diode working and the coil being intact. That's why I did not suggest any particular readings. It's a go/no-go test. Of course, this does not mean they are mechanically sound, but, you've already looked at that and believe that they are. This leads me to believe that you have a connection or a relay problem, not a pump problem. There's nothing in the pump that smacking it around will fix, beyond maybe a tit of crud caught somewhere; but three pumps are not going to exhibit the same issue. The pump is switched on by a relay in the controller (brain box/GICAR/whatever). I think it would be worthwhile to put a meter on that line, right at the relay if you can, and see if the relay is providing voltage to the pump line. If it is, then somewhere between there and the pump there's likely a loose connector. Unlike loose heater connectors, which self-destruct when this happens, lower current connectors just sit there causing problems, often intermittent ones