On Fri, 13 Nov 2009 02:56:45 -0800, RobertL wrote:

We are about to let our house and the landlord's gas safety test has
detected a fault. When the system is shut off from the main the
pressure after at meter drops by about 0.01 mB per second. I think
the pressure was around 20 mB. It was a digital meter.

Now, the first puzzle is that BG and another plumber both passed the
pressure test a year ago when the meter was moved and some pipwork
rerouted. Nothing has been done to the gas system since then.

So a mechanical system that's faulty now was OK a year ago. Why is that a
puzzle? If your car's OK now does that mean it'll still be OK a year from
now?!

The second puzzle is that he said that when he measured it, the
pressur "held OK for a bit and then started to drop".

The house has a mix of copper and old iron gas pipes, all are capped
except at the boiler. It's a 3 bed end terrace.


0.01mBar per second (if that's correct) equates to a drop of 1.2mB over
120s which is within the allowed tolerance for a standard meter and
standard domestic pipework, if appliances are connected.

What's the drop with the boiler isolated?

If it's within tolerance (no discernable drop) with the boiler isolated
then the drop is within the boiler which is OK, though you'd want to check
the gas valve (I'm assuming it's an old boiler) and internal boiler gas
pipework to ensure there's nothing actually leaking in there.

If it drops with the boiler isolated then you need to find and fix the
leak. First port of call is always the hose connecting the test instrument
to the gas meter test nipple :-)


--
John Stumbles -- http://yaph.co.uk

Many hands make light work. Too many cooks spoil the broth.