gas hob fittings

It's best and safest for you to just bring a 15 mm pipe on its own to where the hob is to fitted, and leave both ends of the CORGI plumber to match up, connect and test. The plumber will be more than happy that you've got the major pipework in place for him, and should be over the moon in having to just make all the final connections and installation of isolation valves for you.

Remember to use proper "for gas use" graded copper pipe, and only use proper "for gas use" solder fittings. There is a difference in the two types, so make sure you get them correct.

What is the difference?

Some of the cheaper stuff sold in the plumbing sections of DIY sheds has a lightly welded or compressed seam along its length. Copper for use in gas tight systems is hot extruded, so has no seam. There is a difference.

I've often wondered why iron pipe for gas tends to have a blue "splash" on it - any idea what it indicates?

Seam welded tube? Never seen copper tube like that. Iron, yes, for use as conduit where there is no pressure.

I'd have though something suitable for mains pressure water would also be suitable for gas? (in this respect)

"weight"

IIRC Blue = Medium pipe Red = Heavy Can't recall if there is a code for light but no doubt someone will be along in a minute

AFAIK copper pipe and fittings complying with BS EN 1057 is good for gas. [Which I think is an update of BS 864] It is just possible that some of the sheds might sell non-approved pipe but since I always buy from a merchant and the pipe is kite-marked that's about as far as I bother checking.

I'd have thought any shed with bean counters in charge would have marked any such tube and fittings as not suitable for gas. And probably not suitable for mains pressure water. ;-)

I think this is how the Galvanising splash marks go.

Black markings = External Sacrificial Coating which needs to be laid in a Cathodic bed of mineral salts to prevent or stop external corrosion.

Blue markings = External Non-Sacrificial Coating which needs no Anode or Cathode to be inert in the ground. Slow corrosion response coating I think they call it.

Red markings = External Electrolytic Two Bonded Non-Sacrificial Coating which should be totally inert to rough high mineral ground conditions.

But I could be totally wrong.

With the use of more Polyethylene pipe actually in the ground, the gas co's are only using the slow response coating pipes on the final above ground sections. It could be mainly for its mechanical protection more than anything else.

... snipped

Thanks to all - some more gems of wisdom and another of life's mysteries unravelled.