Stephen wrote:

My old (oil fired) boiler had a 4mm^2 (ish) earth wire that ran from
the copper oil line back to the CU.

That would be the main equipotential bond for the incoming service (i.e.
oil pipe)

When the (non-oftec) plumber recently installed the new boiler, this
was not reconnected. I am having an oftec plumber coming to sign
everything off. Should I connect the earth before he comes and for my
own safety?

All incoming services in metallic pipes should be included in the main
equipotential bonding.

For TN-C-S and TN-S installations this is usually 10mm^2 earth single.
For TT it can be 6mm^2

See:

http://wiki.diyfaq.org.uk/index.php?...ng_and_Bonding

The boiler is earthed but only through the 6A flex.

That is fine.

In my last house the (gas) boiler had all the pipes cross bonded
immediately beneath it. None of the pipes going to or from this boiler
are. I don't think the CH pipes are earthed anywhere. Should they be?

Where is the boiler? Where was it in the last place?

Generally speaking you would expect to see supplementary equipotential
bonding in places that pose an special risk (bath / shower rooms, pool /
saunas etc). There is no harm in have supplementary bonding between its
connections, however there is in many cases no absolute requirement for
it. Note that supplementary bonds do not need to be either earthed, or
connected back to the main CU earth terminal.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/