Have you noticed any decrease in pressure during steaming? Here is a excerpt from someone who had a similar problem that was due to calcification:
- I use the machine mainly for making lattes and at about two per day I made 2000+ before I noticed that the machine would trip my ground fault breaker on occasion. Shortly after that I experienced a random situation where the pump would not produce enough pressure to brew an espresso shot through the reporta filter. Starbucks customer service explained that a calcium build up on the heating element would trip the ground fault breaker and that a similar build up within the pump would degrade the pressure. The obvious solution was to decalcify the machine, which I had been doing every six months. After three sequential treatments the ground fault breaker problem was solved but the pressure output of the pump remained deficient. It would sound normal but before the espresso shot would flow, the pump became very silent and just could not generate enough pressure. Another call to Starbucks customer service and they suggested I purchase a new reporta filter at $30. Before going that route I took mine to a local Starbucks store and determined it worked fine on a demo machine.
- I decided to take the machine apart to see what was inside. The pump is an ULKA Model EX5 which is very simple to replace and can be purchased online for about $50. Before I ordered a replacement I searched this website and found an excellent review of how to repair this pump by Rod Schiffman. This was just the encouragement I needed to try a pump repair. I followed Rod's photo log and with some common tools I was able to disassemble, clean and reassemble my pump. I reinstalled it, primed it before hooking up the high pressure fitting and the results were better than expected. My machine is now working as good as new. Total time to do the repair was less than two hours. This ULKA pump is used in many espresso machines in this category and I suspect that the majority of them could be repaired when problems develop.
This excerpt came from CoffeeGeek.com