Unfortunately you have not given much info to go on re type coach, gas-diesel, year, etc.
However, you stated that "everything works". Not really sure what that means. But, usually, when everything works as normal....lights, radio, fans, etc....but the starter motor only clicks, a common problem is a ground issue at the battery or a loose connection at the solenoid/starter motor. Starter motors draw SERIOUS amperage, especially on diesels. Bad grounds and/or loose connections will easily give the characteristics you describe. Those are easy places to check and good places to start.
You may want to provide additional coach info so that others that have experienced this can provide more helpful suggestions.
2003 Fleetwood Revolution DP