This morning during while pulling the second shot om my Magister Stella I heard the Ulka pump stutter briefly towards the end of the shot. When I tried to pull the third shot it was not working at all, although I could hear the coil humming. At first I thought the intake filter/softener on the supply line might be clogged, so I removed it; the pump just barely was able to move a bit of water for a short time, then quit moving altogether. So, I took the pump out of the machine. It still hums, but does not pump.

My understanding is the electrical part of the pump is simply a coil of wire with an encapsulated diode in series. I put my multimeter on it and it reads the same both directions. Just in case my cheap multimeter was not capable of biasing the diode, I used a second (Tektronix) multimeter...same result. This tells me the diode is likely shorted.

I've replaced one of these in another machine, but sure would like to get Stella running without delay! The question is, is it worth messing with this pump or should I simply bite the bullet and replace it? For example, since the internal diode is shorted, I might get it going by putting an external diode on it. Should I take the pump mechanism apart? I'm guessing these thing are not really repairable and that even if an external diode gets it going, something else may fail sooner rather than later.

Thanks for any insight.

I don't know the Stella, but Ulka vibe pumps in espresso machines don't last forever and aren't that expensive. Yes, a diode is pennies, but if you're going to go through the trouble of pulling it all apart...

Some pumps do not have built in diodes.

Ira

Thanks for the input. This pump does have a diode; it's marked right on the case. This is the same EX5 vibe pump used in a tonne of espresso machines from many companies.

I pulled the pump apart and it was clean...apart from the problem with the coil it should be working. I put it back together, ran some water to it with some hoses, primed it, but it does not pump....just hums.

A new one is on the way.

This is a "toss-up". See this: Diode on vibe pump to quiet it down?

Ulka pumps have a built -in diode whereas Fluid-o-Tec pumps have the diode in the pump's electrical connection "box".