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.
Which is correct?
I am looking to have a new combi boiler installed within the next couple of months and want to make sure the right thing is done.
I won't be installing, it will be a bona fide gas safe installer.
Both. Softened water contains very small amounts of Sodium Chloride (salt) and some boiler manufacturers were concerned about corrosion especially with aluminium heat exchangers. Other boiler manufacturers seem to be happy with ion exchange water softeners so the only conclusive answer will come from the manufacturer of the boiler you intend to fit.
It is not usual to have boiler primary circuits fed with softened water, or indeed have any contact with fresh water..that isn't 'inhibited'.
Boilers and CH are all using closed loops these days by and large
Only the DHW tank gets 'fresh' water into it, and therefore corrosion should be confined to that alone..and its far less a problem than scale would be.
The point of a closed loop is that once the salts have done their bad stuff there are no more salts..so it really shouldn't matter what you fill a boiler primary or CH loop with.
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)
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.
What you've done. Hard water won't damage the primary circuit unless it is leaking. The cold water into the combi for the DHW should be softened, or the plate heat exchanger will scale up.
Be warned; they know a bit about gas and sod-all about water treatment.
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