On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:


However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

As others have said this application calls for a condensate pump. You
shouldn't pipe acidic condensate into a metallic drain system. In the
case of cast-iron I suspect this is as much arse-covering in the event
that the CI finally rots through and the aggrieved owner scapegoats the
boiler installer, rather than a century's natural corrosion. If you are
both installer and owner you may decide not to worry, but you may
still find it hard to get your installer to commission such an
installation. A way around might be to use a condensate-neutralising
gadget (I think Salamander do one).



Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

That's more of a problem: it must not go uphill (otherwise when it does
discharge there's no way for the pipework to empty, and the water in it
will gradually dry out leaving dissolved salts behind, I guess - anyway
I'm pretty sure if you check your boiler manufacturer's instruction you'll
find it says no uphill runs). I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a
heating-only boiler with a separate expansion vessel and PRD which could
be located higher up in the CH system where it could discharge downwards
and out. However that would rule out a combi (because in practice all
combis are system rather than heating-only types - have a look at the
article in the DIY FAQ wiki for an explanation of the different types).

In principle one could remove the PRD from a combi and run a pipe from its
connection point within the boiler to a point conveniently higher up and
re-fit the (or a) PRD there, but this would almost certainly not meet
with the manufacturers' approval (or that of the commissioning installer).

Might be worth talking to your boiler mfr about this - I'd have thought
the question must have arisen. If there's a satisfactory answer please let
us know back here!


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

What is a simile like?