Do you need a 10mm earth to an external oil boiler? Thanks in advance

Depends if it's an extraneous conductive part,or rather the pipe is,as it enters the property

Being as the external boiler has contact with the earth, usually via concrete slabs, yes, there is a small earth potential there. Would you bond the external boiler, or the piping as it enters the house?

The piping is my choice. Then you have the 'problem' where the boiler is on the inside earthing system, and the ground around it may be at a different potential! Insulating sections on the piping? But we then have the boiler CPC exporting the house earth to the outdoor metal unit. I'd go with just bonding the incoming metal pipework, the by-product of that is a very low risk of faults on the boiler not breaking the OCPD, then someone touching the casing while it is live. A low risk, but be aware of it.

Thanks  

Thanks. Appreciate that