On 23/09/2011 13:21, Steve Lewis wrote:

When I installed a salt water softener, I was under the impression
that it was harmful to a combi central heating system if salt softened
water was used inside it, so I installed it bypassing the central
heating system.

I have now read several threads on various web sites saying that it is
ok to use salt softened water.

By "salt softened water" I take it you mean an ion exchange water
softener, that is "recharged" with salt?

(the salt is not added to the softened water - its just used to make a
saline solution to flush a resin impregnated matrix, leaving it charged
with sodium ions. The calcium ion rich water is then passed through the
matrix where it exchanges those with the sodium)

Which is correct?

Some boiler makers recommend not using softened water on the primary
circuit (i.e. the water that is held in the radiators etc). However
since this is not frequently changed the risks would seem minimal.

The water that is fed through from the mains to be heated on the fly and
provided to the taps however there are positive benefits in having this
softened, since this will prevent the plate heat exchanger from scaling
up, and will also prevent scale deposition on showers etc.

(most boiler benchmark books have a space to record the scale inhibition
device fitted in hard water areas. A proper ion exchange water softener
is best, a phosphate dosing device like a combimate will protect the
boiler (but not soften the water), and then there are various electronic
an magnetic devices that make wild claims and probably achieve nothing
at all)

Note there are possibly still one or two atypical combis out there that
don't use a secondary plate heat exchanger for domestic hot water. These
may be better not fed with softened water.


--
Cheers,

John.

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