Thread resurrection here... I was working on a Gaggia today that had low pump pressure. I expected to find a broken spring in the Ulka pump like Joe had mentioned earlier in this thread or a bunch of sediment gumming stuff up somewhere, but instead I found something I hadn't seen before. The threaded plastic keeper at the outlet of the pump (item 3 in the picture) had backed out enough so that the reverse flow check valve wasn't able to work correctly. Screwing it back in and snugging it up brought the pressure back to normal. I love it when I don't have to order any parts to fix stuff.