hi does any one no how to fault find problams on back packs .every time i put a new fuse in and take the setting over number 1 or turn it of then switch it on again the fuse blows 
Before you do any of the below, just check your battery connections are clean and the plug, then check if the wire from the backpack to the battery has not been damaged by getting trapped when inserting the battery, if all ok then do the following.
To do a proper check.......Bypass the PCB board by disconnecting the wire connections to the pump from the PCB and apply power directly to the pump terminals, if the pump runs then replace the PCB, if the pump does not run then replace the pump.