I have a Creda Concept Solaertglo model # 48333. The grill works with the door open or closed. However if you grill is heating up but only a little and very slowly then based on my reading via different forums your voltage regulator is faulty and need to be replaced.
Contact creda Spare parts supplier eg. /www.appliancespartsdirect.com for parts and costs. Ensure they supply fitting instructions.
Chris Mulhall, November 2009