I just got my impressa J9 going after experiencing a similar issue. I found that no water was moving through the system whatsoever and confirmed by removing the outlet hose on the pump and seeing nothing come out. I confirmed the pump was the culprit by taking the inlet hose to the pump off and sucking water through the flowmeter and heat exchanger using my mouth.
I took the pump out, but there really isn't too much to see. I was thinking the pump simply lost it's prime and couldn't get started to pull the water through the system. I decided to submerge the inlet port on the pump with no tube on it into a glass of water and turn it on. Once I did that it all came to life. Reassembled and now it's working flawlessly!