Expansion tank blew up... Help
 

So my expansion tank blew up 2 weeks ago. Ordered a new one, installed it, filled with proper coolant. Let it run, it got to temp, re checked the level, it was topped off perfect. Now I have a new issue. When I'm driving it, around 15 min after it gets to temp, the coolant warning light comes on. Temp gauge reads perfect, pull cap off, level is still perfect. What could be going wrong? Do I maybe need to bleed the system? Maybe air in it? What's odd is I can shut it off, start it back and no light. However 15 min later it will come back on. Possible bad level sensor in the new tank?

Oh, I'm using my older factory cap still. Not sure if that would cause an issue. No coolant leaks from it when it's running so assuming its fine