Just installed a new one. The old one was working, but even though it had no current breakages, it was only heating three lines which was weird. rear demister switch lit up when on, but 10 amp fuse blown. Just put another 10 amp in and it blew straight away? Can't find on tinternet if I should put a bigger fuse in, or have I got an autoelectrician job on my hands d'ya think?