One Core Hotter Than Rest

[chivs688]

I have just installed my Thermalright Silver Arrow onto my i5 2500k.
On RealTemp, it is telling me that my forth core (think that's what it is) is at quite a bit higher temperature than all the others, which are constantly the same.

Is this something to worry about? Is it a problem? Do I need to sort it out?

Thanks.