We've had a combi-boiler fitted, early this year, to drive the heating
and hot water. It seems to be working fine at the moment. The thing
is though that the hot water comes out white and it takes a few
seconds in the sink before it clears.
I know it's only miniscule air bubbles in the water and that they're
harmless in themselves. The question is, what is causing the bubbles
to be present in the water and is it inticative of any possible
problems in the system?
I've had a good check around over the last few weeks and can't find
any sign of leakage.
Thinking about it (though it's probably unconnected) - the central
heating does not have a header tank but is fed from the mains via a
valve. I check the central heating pressure periodically and let more
water in if the pressure drops. The thing is, the pressure does drop
so I'm having to allow a bit more water in every month. Doesn't sound
right to me but I still can't find any leaks anywhere.
Any advice on the significance (if any) of the white water or central
heating pressure drop gratefully received.
Make that three of us :-)
I don't worry about the white these days - it's a lot less noticeable
now the boiler is working properly at last and I can get a high
throughput instead of a pathetic dribble out of it. Lower flow rates
with a high temp just starting to form seems to be the time that the
white shows up. I've wondered if it is scale that forms inside from the
last cycle being broken free in minute particles when the boiler heats
for the current HW demand, but putting it into a glass the water soon
becomes clear so I don't think it can be that.
Both combi's I've had have had slow leak symptoms, but I rent, so I'm
not going to pull up all the floorboards to check the rad pipes. I just
top it up every so often (the new boiler is a lot less prone to this) -
and also, given the filling loop is permanently connected, I wonder if
it is going back through there despite a check valve.
I don't worry about either - I don't drink the hot water, so that's not
an issue, and the pressure drop in the heating circuit is so small as to
be negligible. One thing to consider is if you run the heating very hot
the pressure may build up and the boiler vent slightly on it's pressure
relief valve, mine's custom settable by the boiler engineers - or maybe
a slow leak through the valve. Looking at the vent pipe may indicate if
this is the case.
When I installed central heating, I installed full bore
isolation valves on the various branches. Partly, this was
so I could isolate parts of the system to easily rule it
out of any such leak, but also it was because I installed
it slowly over a few years and wanted to be able to use
parts of the system when other parts were incomplete.
You should inform the agent or owner. They might decide to
have it repaired rather than fixing dry rot in a few years
time. When I rented many years ago, my contract said failure
to report obvious faults like this left me liable for
It's not leaking anywhere near enough, and I pointed it out to the
engineer who sorted the boiler after it was incorrectly installed.
Haven't had to top up since then, so am presuming he did something that
stopped it. I've been here coming up to 11 years now - told the
original landlord, he wasn't concerned, at that point was topping up the
boiler maybe once every few months, it would stabilise at about 1.25
bar, but not sit at 1.5 for months on end (which is how the system was
set when I moved in). New boiler runs closer to 1.75, drops only very
very very slowly, requires much much less topping up, which would
suggest the rad pipework is sound. Boiler bloke pressured the system
higher than 2 initially to check for leaks, nothing obvious then either.
The white bubbles in combi hot water is exactly this - dissolved air
being driven out. It's just because the water has been recently heated
from cold water rich in dissolved gas (air? oxygen?) without any time
sitting around in a tank for the bubbles to come to the surface. If
you heat a kettle of water, you can see the disolved gas coming out of
solution long before boiling point.
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