In article , Martin Angove
wrote:
Then I suppose there's the question of whether it'd be best to
isolate the boiler from the circuit earth when working on it...

On the average copper plumbed house this would probably be
impossible.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser
http://www.sda.co.uk/qsedbuk.htm