On Sun, 31 Aug 2003 19:16:23 +0100, "Margaret Macfarlane"
wrote:
Hi,
Just found this newsgroup and discovered that there are more than 14,000
headers to download so forgive me if this question has already been asked
It has in various roundabout ways, but that's OK.
I have a gas central heating system with 6 heaters. It is at least 10 years
old. When I switch the heating off for a long time (over summer) there
appears to be a large build up of air in the system which gets stuck in the
pump which then needs to be bled.
The build up may well be hydrogen gas, rather than air. Hydrogen is
the product of corrosion of metal components in the system. In
addition to the pump, you would expect to find it gathering in the
tops of radiators. You can easily test whether it is hydrogen by
opening a radiator vent and applying a match or other flame.
Hydrogen burns with a pale blue flame.
Corrosion happens because of the reaction of the heating water and the
metals of the system. It can be almost completely prevented by
adding a corrosion inhibitor to the system and topping it up as
required - typically every three years, or if the system is drained.
At around £20 for the inhibitor (Fernox MB-1 is among the most
common), this is rather a cheap insurance policy.
Corrosion is accompanied by the heating water being brown or even
black and a build up of sludge in the system. A typical place for
sludging is in the bottom of radiators. The tell-tale sign is a
triangular shaped cool area in the centre bottom where the sludge is.
If the trapped gas is air rather than hydrogen, then the cause is
likely to be different - typically air being sucked into the system
through the system vent. This is generally caused by the pipework
not being organised correctly or the pump setting being too high.
It should also be fixed, because if air is pulled into the system,
apart from being annoying, it does promote corrosion.
Scottish Gas came to fix and told me that
the build up of air was actually gas which was coming from various nasty
stuff inside the heaters and provided me with a hefty quote to flush out my
heating system.
Well, what a surprise!. I bet the quote was several hundred pounds,
right? The typical offering is power flushing which involves
circulating a chemical cleaner under pressure around the system.
The margin is outrageous as you probably guessed. BG are notorious
for this. If you do decide to go for this route, shop around for a
fair price.
I had a colleague who was taken for about £800 for this job for about
8 radiators in a flat. The job was bungled and the problem, which
turned out to be something totally different, was not fixed. My
colleague refused to pay and the contractor threatened legal action in
the Small Claims Division of the court. His bluff was called and
the case was dropped. The contractor saddled up and rode into the
sunset.
My question is this: can this be done diy (husband is
quite good at it) and if so what does he need in the way of equipment and
chemicals etc.
There are various things that you can do on a DIY basis.
The first thing is to identify how bad the problem is. The easy way
to do that is check for sludging as described and look for evidence of
poor heating of radiators.
You can also drain the system and remove a radiator to check. Look
for sludge in the radiator. A word of warning. Sludge from
corrosion in a CH system, and the water is a superb indellible brown
dye. If there is a lot of sludge, then power flushing may well
make sense, because there is probably also a lot of build up in the
pipes as well. You can hire the equipment and buy the chemical at
hire centres. Instructions are supplied, and it is a very easy job
to do.
Another approach if there is not too much sludge is to remove each
radiator and clean it by flushing outside with a hose or pressure
washer. You can flush water through the system at each radiator
valve to clear silt from the pipework, again if the build up is not
excessive.
If the system is relatively clean, and in any case after the last
method, you can flush the system and drain it and then refill with a
flushing agent (Fernox and Sentinel among others make these). These
are left in the system for a week while it is run hot and then drained
and flushed.
Finally, in all cases, refill and add inhibitor.
Thanks in advance
Margaret
..andy
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