The jack pump runs at 3000 PSI. IF the pump is NOT producing 3000 psi, the jacks will extend but not have the pressure to lift the RV. You need to have a Pressure test of the pump. IF the Jack solenoids(there are 4, one for each jack) are manually left OPEN and not closed, the jacks will extend to the ground but not be able to lift the RV. These solenoids have "T" handles and must be manually turned 3 or 4 turns, to release. Do you know if this has been done? How long have you owned the unit? Doug
PS, There is NO filter and no limit switch.