On Sun, 23 Dec 2007 16:20:47 +0000, Roger Mills wrote:

In an earlier contribution to this discussion, Andy Wade
wrote:


For reference the full formal gas purging procedure can be found he
http://groups.google.co.uk/group/uk....c770797eeda2e?
dmode=source

Hm - makes interesting reading! I've never seen any of the
'professionals' working on my mas installation get anywhere near
following all that!

Well I confess that if I'm fitting a modern boiler I'll probably skip the
purge step as there is no chance that a flame could propagate back
through the premix fan and zero governor gas valve back into a
combustible mix in the pipes.

If I'm fitting a gas fire, say, I'd have to wait a very very long time
for the gas to come through via the pilot hole. In these circumstances
it's a lot quicker to open the pipework. In which case you need to make
sure enough gas and not too much gas comes through. OK, there's another
short cut, the timbre of the hissing changes between air and gas.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html