problem with G string

Check the action at the nut,- too many guitars these days comes with poorly filed nuts and if the action is too high it will play sharp at the first frets. Fret the 3rd string at the 3rd fret, check how much 'air' there is between the string and the 1st fret - it should be just enough to go clear of the fret.

Here it is demonstrated by luthier Rick Turner in the October issue of Acoustic Guitar:

+1 on the method. Nice to see a visual for it, Steinar.

I'll add: Sometimes when using this method for checking nut setup, I will think I've got a string that is too low (can't see "daylight"). A easy, non-visual confirmation is (while reverse fretting as shown) to tap the string lightly over the first fret. If there is still safe (but nearly invisible) clearance, you can feel/hear the string strike the fret. However, if there is NO tactile/aural feedback, then the string is already resting on the first fret and probably is too low, and that might cause a different problem: open string buzzing.

I'm kinda wondering if the string might hanging up in the nut because he doesn't say weather or not it stays out of tune. I would think the nut would have to be really high on that G string to pull it out of tune. Gonna wait for Bob to chime back in.

Thanks for the replies guys,

I've checked at the nut as suggested , and everything seems fine.
Iv'e lowered the action as much as possible but still no joy.
Which brings me back to the question of string guage.
Will I be able to lower the action more with a higher guage string? ie more tension = less buzzing.
My logic is if I can reduce distance between the string and fret then I wont be able to affect the pitch as much when pressing the string down.

Any thoughts much appreciated.

Bob.