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Can you put softened water into a boiler?

Softened water does not corrode boilers

In the 20+ 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 indeed 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 Can you safely drink softened water?

So what exactly are the real facts about boilers then?

There is nothing to be concerned about with regards to 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.

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

Germany, in the DIN standards, recommends the use of softened water. Germany, in the DIN standards also recommend 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. They are currently trying 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 indeed aggressively harsh and corrosive with a high 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 the use of softened water.

In fact, the biggest manufacturer in the industry, and the only British Manufacturer, Harvey Water Softeners, have sold several hundred thousand water softeners and have never experienced the problem.

‍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. No other country in the world supports the hypothesis that softened water is corrosive. Germany, in the DIN standards, recommends the use of softened water. Germany, in the DIN standards, recommends that chemical inhibitors are not used in domestic central heating systems (yes, you read that right).
"

"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 the use of an inhibitor that is designed for the purpose. The current British Standard 7595:2006 categorically states that you can use softened water with the correct type of inhibitor. 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 the benefits it provides. Use Sentinel X100 as your corrosion inhibitor."

If you are installing one of my softeners, such as one of those 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 works best for you.

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 actually 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...

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.
Harvey interviews Mr & Mrs Parks whose boiler had scaled up, and discusses the impact a water softener had on removing the scale.