Heater blowing fuse

I've had my brava for just over a week now without any problems. I usually use the heater on setting number 1, unless I need to get rid of condensation on the windscreen fast. I've never had to use the heater on fast yet. The problem is if I put the heater above setting 2, it sometimes blows the air out but its doesn't seem to be very powerful either that or the fuse blows. I've replaced the fuse with the recommended one which is 20. Has anyone else had this problem? Or is my heater on its way out? The heater works perfectly on setting number 1. The car itself has done 35,000 miles and is a W reg.

your blower motor may be full of crap, usually leaves. its under the glovebox, try removing it to see if its clean.

failing that, the speed controller is shorting. if you follow the wires from the blower motor they go directly to the speed controller. try replacing it with a scrapyard part (couple of quid)