JG pipe on system boiler?

[SJB060685]

As long as any pipework exposed to the outside elements are sleeved it should be fine, bare in mind you're only going to have maybe a foot or so coming through wall and back into boiler.
If sentinel 500 is an antifreeze then yes, providing you does it right.

 

[EvilDrPorkChop]

I didn't think you could use JG Speedfit on a oil fired system if it was sealed? Only OV.