Shower is tripping the fuse after 5 mins of use.

Check your wiring is correctly sized. I have seen plenty of showers wired up with incorrect conductor cross section (4mm2 and 6mm2 which is barely suitable). Showers should use 10mm2 conductors and use adequately sized MCBs (45A). There should also be RCD protection in place. As the previous responder said, the RCD is tripping, you could have an earth fault. If the your MCB is tripping, then it is likely to be a short either in wiring or in the shower heater/element. Either way, best to get a good sparks in to figure it out.

There is a good chance this can be fixed you can get parts for Mira Showers. Is it tripping the fuse? or the RCD? If it is tripping the fuse is it rated correctly for the shower? This is a 9.8kW shower so around 42A so Fuse should be at least 45A if it isn't that might be the problem. RCD fault would be some sort of Earth leakage and could be the heating element that is faulty. Would need testing to find the exact problem.