RE: Central Heating...

["Kevin Wood" <kevin_wood@xxxxxxx>]

I have just changed part of my heating system and I'm also in a hard water
area.

The main problem I found was some black sludge. I was advised by an
experienced heating engineer to remove reach radiator in turn and
thoroughly
wash it out using a hose pipe until the sludge was gone. Apparently 80% of
it sits in the rads and even if you do flush the system out you can't get a
fast enough flow through them to clear it without removing them.

HSS hire shops have a device to do DIY flushing of a heating system on
their
web site but I couldn't get any information out of them about what it is /
does and didn't bother in the end. It looks like a large pump on a
reservoir
of water with some hoses to connect it to the heating system. I just ran
mains water through the system, opening and closing each radiator valve
until the water ran clear.

As to scale itself I only found this in the hot water cylinder secondary
(cylinder 1/4 full of the stuff!) and I think the old boiler was suffering
this a little. As long as the system is water tight and doesn't keep taking
on mains water from the header tank to replace leakage / evaporation you
won't get too much scale buildup because the water in the system drops its
payload of scale and then stops depositing it.

I hear what you say about flushing opening up leaks. I was advised to use
one of the milder chemicals (P9, I think. Whatever that is.) as my system
is
probably 20 odd years old. I did have a couple of leaks in hard to get
places and used a leak sealing additive to correct this. It seemed to work.

I have a water softener but was advised against filling the system with
soft
water, presumably since it might open up leaks by dissolving scale. It
doesn't seem to have done any harm, however. It's a sealed system and
doesn't lose any pressure.

If I were you, if the system's working OK at the moment, I would flush all
the rads out, maybe flush the system through with a descaler, and fill it
using a good dose of inhibitor, perhaps using softened water. Check that
the
system is not leaking by disabling the supply to the header tank and
checking that the water level does not drop over time.

Scale apparently starts to form with water temperatures of 70 C or more so
run the boiler thermostat at the lowest temperature which gives
satisfactory
heating. I run mine at 55 - 60 C and only turn it up when there's a cold
spell and it can't cope.

Hope this helps,

Kevin