Aluminium Boilers

Consumers Summary

If you are concerned about the corrosion of your aluminium heat exchanger in your central heating boiler that has been filled with softened water, you needn’t be. Please read below for a summary or see the documents on the main Harvey’s site.

The reason for the confusion is that there is a complete misunderstanding and mixup in the market place 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.

There is no evidence from the field that any aluminium heat exchanger has been corroded by the use of softened water. (If you know of one or can find one, please let us know, we would be fascinated to see it).

We have sold hundreds of thousands of water softeners and have never experienced the problem.

All central heating systems should be protected by the use of an inhibitor which 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. You can download a letter from me guaranteeing your aluminium heat exchanger if you have one of my water softeners installed. Harvey’s letter of guarantee.

For the rest of the story, read on:

Technical Information

Prior to 1992 softened water was recommended for all heating systems and there was never any question raised about the potential for corrosion.

When the Committee met for the first time to write BS7593 entitled Code of Practice for Treatment of Water in Domestic Hot Water Central Heating Systems, BS7593: 1992. someone suggested that softened water may not be suitable for aluminium heat exchangers.

There is no technical evidence to support this or evidence from the field. There were indeed extremely few boilers around at that time with aluminium heat exchangers, so under the precautionary principle it was written into the standard that you cannot use softened water in central heating systems.

And thus the myth was born and common sense went out of the window.

Under the principle of unintended consequences it was never anticipated that 15 years later a very high percentage of modern condensing boilers would contain aluminium heat exchangers and thus the market for water softeners would be turned upside down in confusion.

Over the last few years the water softener industry has become more aware of this so when BS7593: 2006 was re-written we made sure we were on the committee. The standard now says that you can use softened water provided a suitable inhibitor is used to protect the system. At the time I thought that was it, job done, we can carry on selling water softeners and everybody will start using inhibitors suitable for use with softened water and aluminium.

But not a bit of it.

The boiler manufacturers, being just as confused as the rest of us, want to be certain that any inhibitor used for softened water passes a performance standard to make sure it will do the job.

The only performance standard available for inhibitors is BuildCert managed by WRC-NSF. That standard only has test procedures for naturally soft water or naturally hard water. Visit them here www.buildcert.com

A procedure for testing the efficiency of an inhibitor in softened water has been written and tested and all that needs to happen now is that it be adopted by BuildCert and accepted by the boiler manufacturers.

Getting everybody to agree and even to meet has been described as like trying to herd cats.

Meanwhile, what do we know for sure:

I personally have sold hundreds of thousands of water softeners and have never ever experienced the problem of softened water causing corrosion in central heating systems including those fitted with aluminium heat exchangers.

I have spoken to most of the experts involved in this debate and not one of them has ever been able to show me or tell me of a first hand experience of actually seeing an aluminium heat exchanger that has been corroded by softened water. They have seen numerous examples corroded by hard water and naturally soft water but never by softened water.

I have spoken to the boiler manufacturers that are willing to talk to me and none of them is willing to show me or indeed can categorically confirm that softened water has caused corrosion of one of their heat exchangers.

The National Physical Laboratory have revised their Guide No. 120 “Avoidance of Corrosion in Plumbing Systems” and there is no mention of softened water causing any corrosion issues (except in the very rare occurrences where it enhances erosion corrosion in hotel hot water loop systems).

I wrote an article in the trade press offering a free exchange for anybody that has an aluminium heat exchanger that has been corroded by softened water and have had no takers. Download a copy here. Softened Water & Aluminium.

If anybody out there has got first hand verifiable experience that they have actually seen an aluminium heat exchanger corroded by softened water I would love to hear from them. Write to me here: harvey@ministryofcommonsense.org

Having spoken with Sentinel, they confirm that their corrosion inhibitor, Sentinel X100, has been formulated specifically to cater for all waters including softened water; which raises the question, how did they test for that?

The Sentinel website clearly states their position. www.sentinel-solutions.net/en/heating/X100/questions

Central Heating Products

X100 Inhibitor

Will Sentinel X100 protect my system if it is filled with softened water?

Softened water, particularly those from household softeners not conforming to BS EN 14743, is not suitable for filling a domestic central heating system unless the water is treated with a high quality corrosion inhibitor. Unlike many other products on the market, Sentinel X100 has been especially designed to cope with all types of supply water, even softened water and affords complete protection.

Can I use Sentinel X100 if I have aluminium components in my system? Yes!! Sentinel X100 was specially developed to protect multi-metal systems, including those comprising aluminium components. Sentinel X100 protects aluminium by ensuring and maintaining neutral pH conditions.

I have also spoken with Fernox, the other major player in corrosion inhibitors and they confirm that they have formulations that would work in softened water but they have not confirmed that their Fernox MB1 is suitable for use in softened water with aluminium boilers.

I am informed that there are corrosion inhibitors on the market that are not very good and everybody is rightly concerned that we need a tough regime to ensure that manufacturers claims can be met.

I am not aware that any other reputable manufacturer of corrosion inhibitors makes a claim for its use in softened water.

Meanwhile, I continue to make my offer that I will exchange, at my own expense, an aluminium heat exchanger that has been corroded by softened water from one of my wonderful water softeners.

As mentioned above, you can find a full writeup of all of our findings here: