John Rumm wrote in
o.uk:

On 25/10/2012 13:21, Alibaba wrote:
harry wrote in
news:56002e72-ef88-4af1-bac1-
:

Why not get a water softener and all you need then is salt?

That's an idea; thanks. I've just been searching for a conversation I
had about this subject a few years ago, and there was a heated (and
inconclusive) debate about whether phosphate dosers and water
softeners were more effective than ion exchange water softeners.
No-one involved in the discussion could point to any controlled tests
to back up their opinions. Anyone got any educated (or fist-hand
experience) opinions on this question?

A phosphate dosing unit won't soften the water. It will stop the scale
precipitation out when its heated, but let the water dry on a surface
and it will still leave marks etc.

In a previous house, I installed a phosphate doser, thinking it would
prevent my heat exchanger from scaling up. One year later my boiler's
heat exchanger was clogged again, as it had done almost every year
previously. Having said that, I think it was partly clogged with iron
oxide (i.e., black rust).

It could clog with iron oxide on the primary side of the HE. There
should be none in the HW side. But that would be a separate problem
caused by corrosion in the heating system.

Perhaps water softeners don't inhibit the
formation of iron oxide. Is there anything that inhibits the
formation of iron oxide, as well as limescale, in heat exchangers
(apart from things like Fernox, which obviously can't be added to
mains drinking water.

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.

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.

You seem to favour phosphate dosers, yes?

Regards,
A