Corrosion report

“Is it ok to use softened water in a boiler?”

This is a question we are regularly asked by customers and installers alike.

Advice has changed over the years, and separating fact from fiction can be difficult without some expertise in the subject. We’ve done the hard work for you with the following information:

The simple answer is yes, it is perfectly acceptable to use softened water in your boiler as long as you observe the following advice from the Heating and Hot Water Council (HHIC):

“Where a water softener is present in the dwelling, ensure that the heating system primary circuit is filled with mains water via the general bypass valve as required in BS 14743.”

Note: A water softener installation must comply with BS 14743 (this states that there must be ‘a general bypass valve which enables the softening unit to be isolated from the mains, while maintaining water supply to the end user’. For installation requirements, refer to WRAS Information and guidance Note No 9-07- 01 “Information for the installation of ion-exchange water softeners for systems supplying water for domestic purposes”.

Put simply, using a water softener is fine as long as you fill your central heating (radiators) with unsoftened water. A reputable installer (ourselves included) will always fit a general bypass valve which makes this process easy.

If you are interested to know how this position was reached, please read on for the full history, our source information and everything else you may want to know on the subject.

 

 

Background to this advice by Harvey Water Softeners

Prior to the introduction of aluminium heat exchangers during the late 1980’s it was considered normal practice to fill the central heating system with softened water whenever a water softener was present in the household.

Up to that date, the central heating chemical inhibitors were designed for use with hard water and the combination of an aluminium heat exchanger and chemical inhibitor led to some corrosion problems. It was therefore put into the 1992 BSI standard for water treatment (BS7593:1992) that softened water should not be used where there is an aluminium heat exchanger.

This led to considerable confusion as many installers and householders did not know whether or not the boiler contained an aluminium heat exchanger so to play it safe most people recommended that the heating system is filled with hard water.

Can you fill your central heating system with softened water?

You can, and there are inhibitors suitable for use with softened water. However, it is advisable to check your boiler manufacturers recommendations and warranties. Many state that softened water must not be used in their systems but some boiler manufacturers using stainless steel and other types of heat exchanger are happy for the use of softened water and some indeed recommend it.

We always fit a bypass valve in accordance with BS14743 so you have the option to fill with hard water or softened water.

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