On 27/10/2012 17:04, Al N wrote:
John Rumm wrote in
o.uk:

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.

Many thanks for your help. Yes, I am in a *very* hard water area. My
primary reason for wanting softened water is just to stop the heat
achangers furring up. Saving money on detergents, shampoo, etc.,
certainly sounds appealling.

Soft will do that. On the down side, it can be its harder to rinse, and
can be a bit more aggressive on plumbing fittings in other ways. They
waste a certain amount of water in the recharge cycle, and you need to
remember to fill them up. Depending on the type you go for (one tank or
two) you may also get moments where it can't keep up with delivery from
the prepared softened water. Lastly they fill a reasonable amount of
space, so you need somewhere to site one. So if going that route, read
up on the types and features before making a decision.


--
Cheers,

John.

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