Gas pipe fitting Q's

Under boards is fine as it is ventilated on the ground floor and enough space under on suspended floors too.

Turn off the gas and undo the meter outlet union. Between the meter horn and the union insert a lid from say a flux tin. This prevents any flashbacks down the pipe from blowing the meter. There is no need to get rid of the gas in a small copper gas pipe. In larger systems the gas has to be pumped from the pipe via a flame trap hose to outside.

In reality a flame trap hose is needed on an installation when purging too. Few are ever used on domestic systems.

As always if you need to ask you probably shouldn't be doing it...

I have seen a flash dow 6 metres of pipe and a boom as the guts of the meter blew.

First time for everything! I've read up a lot (including your FAQs) but there are some areas such as this where I'm not sure. My mind has been made up to DIY mainly because of the incompetence and obvious dishonesty of the "tradesmen" I have had round for gas work in the past, and for quoting for a new boiler.

Through cavity yes, along length of cavity no because of gas build-up. So is it better to avoid under floorboards if possible or is it fine as Drivel says? I have the choice of running the pipe in the corner of the ceiling (unsightly) or under floorboards.

Thanks!

What was the pipe diameter? Pure gas can't go 'boom' as it's concentration is way above the UEL.

A link to BS 6891 can be found under 'gas fitting standards' below. If the under floor space is ventilated then there is no problem, this is common practice. It is quite awkward to get the pipes under the floor in these circumstances. Compression joints should not be used.

installation.

When I cut the old pipe ready to solder the new pipe on, won't the gas mix with air at that point? The old pipe is vertical up a wall and I will be cutting it about a foot from the floor. Won't the gas will rise out of the existing pipe so could be in the 5-15% concentration either above the pipe, or within the pipe?