On 26/10/2012 19:42, Al N wrote:

The primary side, can be dosed with inhibitor like Fernox - you will
not be drinking that. The HW side of the exchanger can be protected
from scale by the phosphate unit. Unless there is something odd about
your local water supply, there should be no iron oxide in that. If
that is proving to be a problem then you need a particulate filter on
the cold supply (BWS do a matching unit with a cartridge for that -
you can get them as a pair from SF)


John, Thanks for the clarification. Thinking back, I think my hot water
taps were delivering luke warm water, which, as you point out, suggests
it was the primary side that got blocked with the iron oxide, thus
stopping the heat getting to the tapwater.

Well you could have poor heat transfer from primary to secondary sides
of the HE because the primary side was blocked by black iron crud, or
the secondary side was furred up with limescale[1]. So you can get a
similar symptom from two different problems with different causes and
solutions.

[1] You may also get reduced flow rate from that as well, but since most
common combis can't heat big flow rates in the first place, you are
probably less likely to notice that in real life.

Yes, now that you've helped to clarify that, I see that my phospate doser
would not have been responsible for that.

So the only real question now seems to be whether to install a phosphate
doser, a salt-filled water softener or an ion-exchange water softener.

"salt-filled water softener" and ion exchange are one and the same thing
IIUC. The salt is used to make a brine solution that is used to flush
and "charge" a resin matrix with sodium ions. The fresh water then
passes through the matrix where the calcium/magnesium etc ions in the
water are attracted to the matrix, and the sodium ions in it are
attracted to the water. Hence one set of ions gets swapped for another.
(and contrary to popular expectation, the salt is not not added to the
domestic water - its just used for the flushing process)

You seem to favour phosphate dosers, yes?

Favour would be the wrong word - they do different things (well one is a
reasonable subset of the others).

There is also a big difference in installation cost (although you may
find the effects of a real softener will eventually pay for themselves
in reduced detergent use etc).

Whether you want to go for fully softened water will depend a bit on
what you want to achieve and why. Some folks are not keen on soft water,
anyway - although if you are softening a naturally hard supply, then at
least you have the option of using it "raw" as well for drinking etc.




--
Cheers,

John.

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