My microwave (Rank Arena, RAMW23) is not heating up food anymore. Where the time is located on the screen, under the hour column, there is a code "lS" (in red and underlined), so I'm not sure what this means or how to correct it as there is nothing in the manual to clarify what this is... Could you please assist as I don't want to have the expense of buying another microwave when this one isn't long out of warrantee? I am expecing a microwave to last longer... Thank You, Mrs Wilkins.