3.15A and 4A fuses - can I swap?
First, replacing a fuse with one of a higher current rating is a bad idea.  In this case, assuming the two fuses were the same type (fast or slow blow), then there is definitely something wrong with your scope.  Since the scope is not meant to exceed 3.15 A, but actually exceeded 4 A, there is clearly something wrong.  By making it take more current before the power was shut off, you may have even damaged it further.

This is all assuming the two fuses were of the same type.  If the original was a slow blow, and the new a fast blow, then what you observed could still happen in normal operation.  Look at the old and new fuses carefully.  This isn't universal, but usually a fast blow fuse is just the melting link suspended between the ends.  A slow blow usually has the melting wire wrapped around a ceramic rod.

If the original was fast blow and you replaced it with a slow blow, then there is really something wrong with the scope.