"Martin Pentreath" wrote in message
...
Hi,

I have a non-condensing combi (Ariston Microgenus) from which there is
a slow but constant drip from the 15mm pipe sticking through the wall
to the outside (which I think is for emergency pressure relief?). The
pressure gauge on the boiler is at 2 bar, which is within its
tolerance range. So why is it dripping and what should I do to stop
it?

Cheers!

Martin

It will eventually lose pressure. In my experience, once they start leaking
they can't be cured. But, it might be worth twiddling the knob on the valve
(usually a green ridged plastic cone) which will release some pressure and
might flush debris away from the seat. They start leaking for one of three
reasons. 1, someone has twiddled the valve and let debris into the seat. 2,
the system has been overpressurised during topping up. 3, the expansion
vessel isn't functioning correctly which in turn means either the diaphragm
has gone, or it needs topping up with air: see the Wiki.
(http://wiki.diyfaq.org.uk/index.php?title=Main_Page and also
http://www.makewrite.demon.co.uk/SealedCH.html).

Replacing the valve isn't usually difficult provided you are happy to put
spanners on plumbing. Spares are cheap from BES; make sure you get the right
gender for the inlet and outlet threads. You need to depressurise the system
to do this.