How can i fix my Triton Ivory 2 Shower. It keeps tripping out?

When i turn the shower unit on it just trips out, which trips the electrics in the house. If i turn it to the cold setting the shower remains on. As soon as i turn it to a hot setting it trips out. Only started this last night. I've been reading FAQs and forums and i think its either the PRD or thermal cut out. Any advice?