In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:


Questions:
1. Can an unflushed system cause a cast-iron heat exchanger to leak
after 14 months (unless there's a manufacturing fault)?
2. If there isn't a by-pass circuit, could all the valves being up to
temperature have caused enough pressure to rupture the heat exchanger?
3. Would a long layoff or low level of usage have exacerbated this
problem?
4. Who's at fault here? The boiler's manufacturer's, or the
installers (name-and-shame time: Merseyside Central Heating of
Crosby)?

I would be surprised if a decent heat exchanger would corrode enough to leak
in 14 months with as little usage as you indicate - whatever you did to it!

Black water indicates that corrosion has taken place at some time. This
could have been there for a long time, and not been flushed properly when
the boiler was changed - or it could have happened since the new boiler was
installed if there was no inhibitor in the the system - or if *lots* of
oxygen had been introduced.

I guess that it is probably a vented system - with a small fill & expansion
tank in the attic - and that it wasn't converted to a sealed system when the
new boiler was fitted. Is this correct? If so, is there any evidence of
pumping over - in other words, when the pump is running, is there a constant
flow of water out of the vent pipe back into the F&E tank? If so, this would
be a good recipe for rapid corrosion!

Assuming that the boiler is correctly vented - with a clear path to the F&E
tank, not interrupted by any valve - there's no way that the pump can
generate enough pressure to do any damage - even when running stalled.

I wouldn't have thought that laying the system up would do any harm.

Apportionment of blame could be a bit of a challenge - because the boiler
manufacturer and installer will blame each other. Start with the installer -
the black water has *got* to be down to him due either to:
* insufficient flushing
* not putting inhibitor in, or
* incorrect system design

or some combination of these.

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.