Shower Pump keeps blowing fuse?

I have an Aqualisa Mach 340 shower pump which has been working fine for the last 3 years until alst week when the plug fuse blew. I changed the fuse and that blew as well. After the 3rd fuse blowing I am certain that there is something wrong with the pump but I don't know what. I called Aqualisa and they said it could be a fault with the impeller sticking and that I would have to pay them £81 for a call out fee.
Can anyone suggest how I can check this impeller and also if there could be anything else that is causing the fuse to blow.
Thanks