I'm a bit perplexed, and so, am hoping for some help.

My setup: plumbed Duetto II (~4yrs, only owner).
Water is via a Mavea Purity C Quell ST 300

Pump seems to run and I can draw water through the group and the hot water wand. Machine is heating up well

Problem:

After making a couple drinks Saturday, I flushed water through the steam boiler (until the pump came on to refill), and then the pump kept running and running until it shut itself off and triggered the alarm. I removed the fill probe and cleaned it well with 600-grit sand paper. That seemed to solve the problem, initially, but after having the machine on for about an hour, the problem recurred...so I shut it down for the night. Today (Sunday), I checked the stainless mesh filter (between the pump and the intake solenoid) and it was clean as a whistle. So, I removed the solenoid coil and valve, cleaned the valve thoroughly and then put it all back together. The machine seemed great for a few hours, and I checked functionality several times by flushing the steam boiler. After being on for about 8 hours, I made my wife a latte, then flushed the steam boiler once again and the pump wouldn't shut off...until the alarm activated again.

One thought I have is that what I hear, when I think I hear the pump, is actually the motor...and that my pump is actually failing intermittently. However, I do see the pressure gauge jump to 9 bar during the process. So, I wonder if the solenoid is failing intermittently?

Any ideas what could be the problem would be appreciated.

Clean up probe(water level probe) with acid.

Thanks for your reply! I was already resigned not to receiving one.

I polished the probe already. Beforehand, I checked conductivity with my multimeter and there was a segment running about halfway up from the tip that was not conducting. After polishing, it conducted well all along its course.

The machine works fine, except that I have to shut it off after each session to let it cool down for a period of time so the steam boiler will autorefill (which it does reliably after the cooling down period).

I've come to the conclusion that it's either the solenoid coil overheating and failing or it's an electrical overheating problem in the Gicar controller. In either case, the solenoid inlet valve is not opening as it should, so the pump is running against a closed valve until it triggers the alarm. Once the machine cools, the inlet valve opens as it should and the boiler actually refills.

I've got a new solenoid coming from CCS...but like an idiot, I elected to accept the "free shipping" instead of paying to get it here faster, so I have to wait until Monday to get it I guess if that doesn't solve my problem, I'll be replacing the Gicar controller.

As I suspected, it was the solenoid coil.

Yes it could be solenoid coil...which kind of solenoid coils do u use...please dont tell u use Parker solenoid coils? XD