Thanks Dave. Before I read your last post I decided to go ahead and see if the fill quantities were OK for the remainig bottles. I just had enough time (before I run to pick-up my daughter at school in 15 minutes) to test bottle 2. The fill quantities at each of the 15 preset amount resulted in fill levels of between 2% and 11% over, with the smallest fill level (i.e., 60ml) being 8% under. Now this is more like it! What's particularly gratifying is that the fill levels are almost always over, which is far better than being under (as I found with bottle 1). I think I'm safe to conclude that the pump is fine and that I have a leak at chemical bottle 1. On close inspection, I think the most likley candidate is the gromet/seal in the center of the lid on bottle 1 (where the temperture probe is inserted). The seal seems loose. Do you think vaseline will do it, or is replacement the safest option (I don't even know if these parts are available)??