Hugo Nebula wrote:
Assuming they put the full bottle in and no more, is this
enough for a seven radiator system?
Yes. There's a moulding date on the bottom of the Sentinel bottle,
which might give you an idea of it's vintage. I dosed my system
yesterday, the bottle was moulded 11 months ago but had been in the
garage for 4 or 5 months awaiting tuits. And they should have completed
the self-adhesive label on the bottle.
I'm not hopeful of getting a response from the installer. He's got
his money, and wouldn't respond to my concerns about the system last
year.
You've got to ask him, though. Maybe a letter with a copy to the
manufacturers. A copy to the local press if he blanks you. I'd be
mortified if something I'd done failed witin that time. I also believe
that you'd still have a claim, in that it should have lasted much
longer, even though the 12-month guarantee may have expired; that's one
for UK-legal.
Questions:
1. Can an unflushed system cause a cast-iron heat exchanger to leak
after 14 months (unless there's a manufacturing fault)?
I'd think I could get it to fail that quickly, but I'd have to try
really, really hard.
The problem could be 1) dissolved oxygen due to
a) pumping over (as mentioned) and/or
b) galvanic corrosion. I'd guess pumping over.
It might also be 2) fireside corrosion due to low return temperatures
(assume it's not a condenser since it's CI).
Given the evidence of corrosion, I'd think we're talking about 1a or
1b.
You could plug the hole with that epoxy putty stuff, refill and set the
system running, WITHOUT firing the boiler, to see if you can get it to
pump over under any conditions. If so, I'd reckon it's negligent
installation. The 'by-pass TRV' shut condition would probably be the
worst case for this. In fact, all TRVs shut, but pump still on, might
be the worst possible case, depending on where the cold feed and open
vent connections are, see below.
You could also get a sample of the water in the system (unless it's all
been diluted or drained). Low pH (less than 7, acidic) would be the
worst case for galvanic corrosion. This could be caused by great gobs
of active flux, inadequate pre-commissioning flushing and/or no
inhibitors. Ideally it should be around 8 or 9 (alkaline). I'll see
what pH my system is, out of interest, if I can find some litmus paper.
If you know anyone in secondary school, the chemistry lab technician
would test a sample of it for them & marvel at their sudden interest in
applied chemistry.
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?
No. The pump's maximum differential pressure (at no flow) is tiny.
You'd need great pressure which you can't get with an open system. You
could get huge pressure, easily, on a sealed system, with no expansion
vessel & no pressure relief valve.
If there's black sludge (magnetite) it's likely corrosion. However,
with all TRVs shut, the flow rate would decrease and the pump
differential pressure would increase. This might start pumping over,
although there may be none under normal flow conditions.
3. Would a long layoff or low level of usage have exacerbated this
problem?
No.
4. Who's at fault here? The boiler's manufacturer's, or the
installers (name-and-shame time: Merseyside Central Heating of
Crosby)?
Could be a manufacturing defect but the installer would be my prime
suspect. A new boiler might be simplest to get Mum's heating on again
asap. I'm not sure you could get these boilers still (non-condensing
presumably).
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