Low water flow from the tank through the screen

I have serviced my Jura E8 and reassembled it successfully. It made coffee for a week and then started having a water flow problem. I ended up ordering a new pump and membrane regulator. I have tracked the problem to the intake screen at the base of the water tank. If I depress the plunger valve manually while holding the water tank, it flows freely. If I disconnect the flowmeter end of the first tube and install the water tank, the water trickles out drops at a time. The screen has been descaled and appears to be clean, and all the o-rings and seals have been replaced. Is there a common reason for low water flow through the intake?