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Can you put softened water into a boiler?

Softened water does not corrode boilers

In the 24+ years I've been around this industry, I've seen the impact of two myths specifically that have caused a lot of concern and confusion to consumers:

  • The myth that you cannot drink softened water
  • The myth that softened water corrodes aluminium boiler heat exchangers

Both of these are factually incorrect.

It is perfectly safe to drink softened water, and indeed, according to the World Health Organisation (WHO), softened water is considered wholesome and conducive to good health.

For more information on drinking softened water, I have written a very detailed page about this on my website - Can you safely drink softened water?


So what are the real facts about boilers?

There is nothing to be concerned about the corrosion of your aluminium heat exchanger if your central heating boiler has been filled with softened water.

Worcester Bosch, after 18 years, has never been able to show the industry a heat exchanger corroded by softened water.  This myth predominantly sits with Worcester Bosch and Ideal Standard, although, unsurprisingly, who you speak to on their call centres will depend on the advice you are given by however clued up the individual is on the phone (as at February 2023).

No other country supports the hypothesis that softened water is corrosive.

Germany, in the DIN standards, recommends the use of softened water. In the DIN standards, Germany also recommends that chemical inhibitors are not used in domestic central heating systems.


So how did this confusion all begin?

The reason for the confusion is that there is a complete misunderstanding and mixup in the marketplace between the boiler manufacturers, the corrosion inhibitor manufacturers, the industry certifiers and the domestic water softening industry. Much work has been done to get their act together to clarify the situation.

Meanwhile, here is what you need to know… While naturally soft water found in areas such as Scotland, Wales and Cornwall is aggressively harsh and corrosive with a more corrosive pH, artificially softened water with an ion exchange water softener is not corrosive.

There is no evidence from the field that any aluminium heat exchanger has been corroded by softened water.  Yet the myth persists.

The biggest water softener manufacturer in the industry in the UK and Europe, and the only British Manufacturer, Harvey Water Softeners, have sold several hundred thousand water softeners and have never experienced the problem, yet have encouraged their customers right from the start to soften the water in their boilers.

‍What does Harvey Softeners have to say?

Here's what Harvey Bowden, chairman of Harvey Softeners, has to say on the subject:

"I have never seen any evidence of a central heating system corroded because of softened water
and I’ve been here for over 40 years. I have never heard from anyone who has experienced corrosion from softened water. Worcester Bosch, after 18 years, has never been able to show me a heat exchanger corroded by softened water.

I have heard from many of you that say they never use corrosion inhibitors and they still don’t get any corrosion of aluminium or any other metal.

All central heating systems should be protected by using an inhibitor designed for the purpose. The current British Standard 7595:2006 categorically states that you can use softened water with the correct inhibitor type. There is an inhibitor on the market specifically designed to work with softened water, Sentinel X100.

So the common-sense position is this:

Use softened water in your central heating system and enjoy its benefits. Use Sentinel X100 as your corrosion inhibitor.

If you are installing one of my softeners, such as one from the Minimax range sold by Hydroworks, you can download a letter from me guaranteeing your aluminium heat exchanger."


What advice can you give?

If you are not installing a Minimax water softener made by Harveys' and want to cover yourself with the best advice, well, I would personally read between the lines what has been said above and make a decision that sits best for you.  Basically make your own informed decision.

You may find the following consumer guide helpful: Protecting your boiler & heating system.

Furthermore, the UKWTA (UK Water Treatment Association) has published an excellent document which was researched independently by the European Water Treatment Association entitled Softening Water Does Not Increase Corrosivity.

You may also wish to watch the following videos for some extra helpful information...

Scaled heat exchanger comparison – Harvey Water Softeners.
Harvey presents to the Boiler and Water Inhibitor industry the findings of the BSI independent testing. To demonstrate the importance of the results, this event was held at the House of Lords in London.
Harvey shows the industry around the testing facility at the BSI (British Standards Institute) independent testing facility