If it keeps doing it you have a DEAD short to earth.
Take the fuse out again, disconnect the pump, then do a CONTInUITY TEST BETWEEN THE FUSE OUT terminal and the EARTH.
There should be NO CONTINUITY but I bet there is.
Easy way to tell the out terminal is with fuse out see which one is live, ie supply, then it is the other one(terminal).
If there is continuity you have the wire going to earth somewhere, ie touching the body somewhere.
tabetha