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Will softened water work with my heating system?

Water Softeners and Domestic Heating Systems

It is commonly believed within the plumbing industry that water softeners and central heating systems do not mix.

Ask almost any plumber in Kent and they will agree, often pointing out that softened water can damage a customer’s central heating system. They may also point out that any warranty could be invalidated if softened water is used with a boiler containing an aluminium heat exchange plate. 

But when pressed on exactly WHY softened water could cause a problem, the answer is usually much less clear, something along the lines of  “because the boiler manufacturers say so”  accompanied by a quick shrug of the shoulders! 

And who can blame them? 

The City & Guilds Plumbing and Domestic Heating training course dedicates a pathetic 3 pages to the subject of water treatment. 

Even a quick glance of the relevant British Standard BS7593 does little to ease the confusion, stating that “…naturally soft and base-exchange softened water have an increased potential for corrosion and the primary circuit should not be filled with softened water unless a corrosion inhibitor specifically formulated for the purpose is added. And that softened water should not under any circumstances be used where a boiler contains aluminium”

So why is there so much confusion? 

Naturally hard water contains calcium and magnesium together with bicarbonate, sulphate, chloride, nitrate. A water softener simply swaps the calcium and magnesium ions for sodium ions. The bicarbonate, chloride, sulphates (the anions) are NOT removed and the alkalinity remains unchanged. 

Naturally soft water, on the other hand, contains very little dissolved solids; its pH is often low and buffering capacity is negligible. Hence, naturally soft water is often very corrosive to metals.

When BS7593 was drafted in 1992, there was a misconception that NATURALLY SOFT water and ARTIFICIALLY SOFTENED water are the same thing. They are not. 

In the past, some boiler manufacturers have reported cases of corrosion issues where a water softener has been fitted. It is important to note that when Worcester Bosch and Harvey Water Softeners Ltd have worked together on this issue, every single reported case (18 in total) was proven  not to have been attributed to softened water. 

FACT: Installing a water softener will not produce water that can damage your boiler or central heating system. 

Ok so that makes sense, now show me the science to prove it!!

Throughout the world, the water softening industry’s trade associations such as UKWTA, EWTA and WQA have never seen a single case of corrosion failure. 

In 2012 this was categorically proven by the UKWTA who conducted a study using two identical test rigs consisting of a boiler, radiator circuit and a set of corrosion coupons. One was filled with mains hard water and one filled with softened water. It concluded that  “over the life time of a modern central heating system, filling with base exchange softened hard water mains would appear to present no significantly greater risk of corrosion of system metals than filling with hard mains water”


Use the right corrosion inhibitor

Another option for you is to use Sentinel X100 corrosion inhibitor which is specifically formulated for use WITH softened water.

What is the official position of my Boiler Manufacturer?

Harvey Water Softeners have produced a boiler_manufacturer_survey to check what your boiler manufacturer says.

One water softener manufacturer in particular – Harveys –  will GUARANTEE against boiler corrosion and will replace your boiler free of charge in the unlikely event of corrosion occurring!

To Summarise…

  • British Standard BS 7593:2006 States you CAN use softened water to fill a central heating circuit with the correct corrosion inhibitor
  • There is NO proof that softened water will corrode a boiler
  • A water softener can be installed in ANY home, regardless of the type of heating system
  • Use Sentinel X100 corrosion inhibitor
  • If you are unsure, your plumber simply needs to open the bypass when filling the primary circuit.

Book a water system service here!