I was talking to somebody today who was bemoaning the fact that, as a
residential property landlord, he had this year changed the CORGI who
performed the annual gas safety inspection on a flat he lets out, and as
a result, found himself with a whole lot of extra work needing doing.
Apparently the installation got condemned because the gas feed pipe was
of too narrow bore for the demand; and to gain the certificate, he had
to have it replaced with bigger-bore stuff. The theory being that
inadequate gas supply could lead to CO formation I suppose? I don't
know what gas appliances are in the property.
Does this sound plausible? I thought that use of too narrow a supply
pipe just meant your appliances worked at less efficiency, not that it
was a safety issue?
So - just wondering which CORGI was at fault - the original one who
apparently failed to spot a potentially lethal error for several years,
or the new CORGI for his fraudulently insisting on unecessary work?!
On Sun, 25 Jun 2006 17:38:10 +0000, Lobster wrote:
Not at all likely to happen.
The real danger with inadequately sized pipe is that when the boiler fires
up it may cause a ring on the hob to go out, which then spews out unburnt
Regardless of the potential interaction between appliances I've described
above, if the working pressure at the inlet to the boiler is less than
its burner's working pressure it would be a cause for concern and
should possibly be designated At Risk.
It's a grey area. As far as I can recall (without traipsing out to the van
to consult my guide) the CORGGI guide to assessing unsafe situations such
as this doesn't explicitly mention this scenario, therefore it's a matter
for the fitter's judgement. In the trend to arse-covering prevalent in
more than just this industry (cf surveyors' reports) it's safer for the
installer to fail than to pass the installation.
On Sun, 25 Jun 2006 21:21:23 +0000, John Stumbles wrote:
The correct pipes are those that only drop 1 mbar between the meter and
all the appliances when all the appliances are full on.
In practice a substantial majority of UK domestic gas installations would
fail the absolute "by-the-book" standard as laid down in BS 6891 (link
below). There are a number of helpful factors.
1) The meter almost certainly gives 21-22 mbar for most people most of the
2) The meter standard has been relaxed in the last few years to 19-23mbar
which means that appliances are expected to have gas delivered at over
18mbar. This means that in practice there is (informally/ de facto)
3mbar for the pipes.
Against this is (as Drivel correctly states) premix burners are less
tolerant of under gassing. Also in extreme conditions (e.g. a JCB+gas
service pipe incident) the pressure at the meter might fall to 15mbar
giving only 14mbar at the appliances or less with poor pipework.
For the installer the 'risk' for not making the user/owner aware of the
problem can be large, in the worst case. It could result in the fitter
having to replace a lot of the installation pipe work with 28 or even 35mm
pipe. This would be at the fitter own expense, on pain of losing his/her
OTOH any fitter who applied every jot and tittle of the regs would have
about one customer a week (either because others would be more popular
with the landlords or because it would take a week to get everything
Over gas leaks, flueing, ventilation, safety controls and other more
direct concerns, a less pragmatic approach will be taken.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Drivel? You have a cheek. As I recently pointed out your FAQ is a shambles
of misinformation, which looks like it was written in 1986, and half the
time you clearly haven't much of a clue for a so-called professional. It is
bad enough dealing with the amateur uk-d-i-y Lunatic Association on here,
who give appalling advice on matter they know sweet FA about. I am not on
here as a buddies club to speak to the idiots. It is to give solid advise
top people who request it.
I feel sorry for the poor bastards who read your sadly lacking FAQ and
It is certainly plausible. An undersized pipe will result in too much
pressure drop between the meter and the appliance. This will affect
different appliances in different ways. It could certainly affect the
gas / air mixture and hence the production of combustion by products. It
could for example starve an appliance of gas - perhaps causing a hob to
extinguish when a boiler fires up.
Hard to say without more detail (i.e. list of appliances and their power
ratings, plus a description of the pipework (i.e. length, size, number
of bends etc)
It is not hard to size gas pipework. A quick measurement and
calculation for a few installations would show whether the pipework is
undersized and whether CORGI 1 or 2 cocked it up.
Presumably CORGI 2 found the burner pressure dropped below the minimum
specified value with all the appliances going?
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.