I have a La Cimbali M21. When I stop the pump, I usually get a sucking sound and liquid coming out on the tray. About every other time I stop the pump, the suction is very weak and water gets left behind in the portafilter.

I assume this is the back flush and associated with the 3-way solenoid?

I have a feeling that I need to open up the group head and clean the 3 way solenoid. Can you please confirm? Is this too hard to do and what part should I order so as to minimize the downtime?

Thanks
Zee

When I made coffee this morning, I noticed again that the first time I stop, the back flush seems to work. I turn it on after a minute for the second cup, it does not backflush well (soapy puck).

I decided to clean this with the machine cleaner (http://www.amazon.com/gp/product/B004L8TN3M) and the backflush worked everytime (I turned it on and of about 7 times). When I did this without the cleaner, it worked fine as well..

Need some deductive help here