logical thinking as always JK the pump unit fits in tank at about 45 degrees so I cannot see how it can be upside down, also my first thought, but pipe bends/location prevent it from fitting any other way , top/body cannot spin either, Caterham advice is not to bother earthing but have tried both earthing tank, and earthing top of pump, no change, with pump properly orientated (as far as I can tell) with float at bottom of travel, the sender reads IRO 100 ohms, with float up reads IRO 4 ohms, I suspect it is possible to re-cal the Stack , but all the stack should have seen is that the power has been off for a while, all other readings, Oil pressure, water temp etc are fine so don't want to go there just yet. it has all the hall marks of me being stupid but after several coffees I have not spotted anything, just going to see if I can find an electrical diag and see if it has any resistances for full and empty, The only thing I have done is removed and refitted the float arm, but again it can only go back on one way . Tim