Fry Filtering Device units filter pump wasn't pumping oil. customer said they filtered two vats last night but not the third. It didn't when I checked. I tried to put flexible hose in to see if there is anything clogged inside the vat or oil drain. also possibility of having filter pan clogged especially when I turned filter without hooking drain pan. I can hear air been pumped to the vat. had customer clean drain pan and tried to filter other vats, left and middle since they were up to temp. they filter fine. waited for the right one to get up to temp and filtered it too. everything is working and pump is pumping oil, operation okay.