central locking-not working on hot days
 

Hey all,
I hope someone can help me, I have a 2005 NF sonata that will unlock with the central locking perfectly well on cold days, but has trouble on hot days.
Two doors don't unlock and another is getting worse. It seems to me that something is stretching in the heat and just not pulling the mechanism enough. Has anyone had this, and is it something I can adjust or fix. Thanks in advance
Trev