If the fuse keeps blowing there is a problem somewhere with either a bad connection or in the wiring in the seat heater circuits themselves. Something is causing higher amperage in the circuit to blow the fuse... google search Ohms law to help understand how voltage, amperage and resistance affect eachother. The voltage is constant so you have a starting point for figuring out where to look.

Fuse weirdness
 

Bumping an old thread. My X5 front seat heaters aren't working, as described here. But...if I pull the 25 amp fuse and leave the 5 amp, lights come on for two or three seconds then turn off. Put the 25 amp back in and no lights. Fuse doesn't blow, but switches die. Pull 25 amp fuse again, and lights come back.

This seems weird.