NewTeam 1000XT causes fuse to blow?

The electric supply to the shower comes through a fused (3 amp) switched junction box. It has been working OK since installation, about 2 years ago. Recently the in-line fuse blew. The first time it happened I only noticed when I came to use the shower one morning - it had been OK the day before. I replaced the fuse and used the shower OK, but about 2 hours after switching the shower off, the fuse blew with a big bang. I replaced the fuse and used the shower OK, but switched off at the junction box after use. This seemed to be OK for a few times but the last time the fuse blew when I switched on at the junction box prior to using the shower. What is odd is that the power line into the shower goes to a connector and then to the shower operating switch which had been in the off position when the fuses blew. I cant see how a short could arise - there are no leaks of water into the internals of the shower body housing the pump etc. Any ideas?