Hi Peggy, This one has me stumped. Pump works fine in wet mode. When I switch to dry pump, the pump lever has to much resistance. It will not go down without constant pressure on the knob. I then disconnected the hose from the bowl rim to the side of the pump. Placed a can at the connection end to catch any water, and pumped. About 1 cup of water came out (of the pump side). Was then able to pump the bowl dry with no resistance. When I reattached the hose and pumped, no resistance was present. I then poured some water into the bowl and pumped it dry with no resistance. I disassembled the check valve assembly to make sure everything was working. It appears to be fine. I did rebuild the pump about 3 weeks ago as it was shot. I then opened the seacock and wet pumped the head. Again no problem. Whe I try to pump it dry, you quessed it, the resistance is back. My tank vent is clean with no blockage. HELP!!!