Saturday 17 April 2021

Corrosion, let's go with nature, not fight against it

VDI2035 is becoming more and more recognised in the UK heating industry, I have been banging on about this method for about 8 years, so it's good to finally see it been used more in the UK, both in the Domestic and Commercial side of our industry, but what are the requirements of VDI2035? I will try and explain these using methods used by my preferred brand Elysator, other products are available.

VDI2035 identifies 3 key parameters required to cause corrosion in heating and cooling systems

1. Dissolved Oxygen

2. System water with high conductivity

3. Low pH

Elysator products work with how metals are naturally inclined to react, not against them, harnessing the effects of these natural reactions and applying them to the benefit of system protection

The Science: let us delve a little into the science of corrosion, A typical heating system can be made up of a variety of materials, copper, brass, various forms of steel, composite and even plastics.

All metals contain negatively charged particles called electrons, the number of electrons in a metal define how stable that metal is, many metals in their refined state, do not have a stable number of electrons, instead they have a surplus of electrons and will readily give up these electrons to become stable, conversely, Oxygen requires additional electrons for it to become stable, so metals and oxygen exchange electrons to achieve greater stability.

Chemists refer to these processes as Oxidation (loss of electrons) and Reduction (gain of electrons) the more common term for this process within metals at least is corrosion and for iron and steel it is better known as rusting, the presence of oxygen in the water of a heating system therefore creates a favourable environment for corrosion to occur 

let's look at ways we can address this naturally occurring process.

Oxygen is and always has been the enemy of a heating system, so it's always something we should deal with, in my opinion on installation the best way to do this is good design, using good quality materials, correct expansion vessel sizing and correct pre-charge of the vessel as well as a good maintenance regime, if dissolved oxygen is a problem within the system, there are ways to address this using Elysator products, I will go into this in further detail a bit later

System water with high conductivity: a lot of the UK has hard to very hard water, water has minerals and salts in them, it is these that create the conductivity, different areas in the UK have different water hardness, so each area will have different needs, but whatever the water, if we remove these minerals and salts on filling, we lower the conductivity, basically restricting the path that is needed for the chemical reaction that is needed between metals, water and oxygen for the corrosion process to take place, so rather than adding a chemical to try and stop the natural process of chemical reaction that creates corrosion, we just remove the pathway, the best way to treat heating water on filling is using a demineralisation unit, basically a mobile cartridge that you just connect inline with the mains water fill point and the filling connection to the heating system (as in image below)

Filling the heating system with the Elysator Purotap Leader using the Nexion cartridge has the additional benefit of raising the pH of the initial fill water to around 8.4, the salts and minerals are removed from the water through an ion exchange with the resin, the Nexion cartridge has a surplus of anion resin and it removes free carbon dioxide which raises the pH of the water, this give you water suited to a heating system, with all the potentials to allow corrosion removed, so lowering the risk of system corrosion massively, without the addition of any chemicals

Purotap Leader
Ongoing protection: To ensure that the system water stays at its optimum its important to ensure any future top up water is also dimeralised, there are options for this depending on the size of the system, there are several options, I will cover the main ones. For small domestic systems there is the Purotap Micro, a small relatively cheap cartridge, that gets left on site, allowing the quick fill to be connected to it so any top up water passes through the Purotap cartridge demineralising the water before it enters the heating system, these are not designed to be left under constant pressure, so need to be disconnected after filling.

Purotap Micro

For larger systems there is the Compenso units, these can be connected to the system and can be left under pressure or connected via a pressurisation unit if required, so any water filled via the pressurisation unit is demineralised, these come in different sizes depending on system volume 2 - 50 litres 

Purotap Compenso

Continued Protection: For systems that may have oxygen ingress, or ongoing issues, or you just want to ensure the water remains at its optimum, Elysator have reaction vessels containing high-purity magnesium anodes, there are different size units which will depend on the size of the system it is connected to, there are units to suit dometic up to large commercial systems, the working principle is the same for each, so I will list the units available, then I will run through how they work, for me, now I install heat pumps, which are expensive items to spend some additional money to ensure protection of the heat pump is a no brainer in my opinion,  or commercial plant rooms where again the plant equipment is costly, it's worth ensuring these components are fully protected.

For this Elysator have several option, for the domestic market they have the SorbOx, these are suitable for system power up to 30kW and system volumes up to 800L, and are design to be installed in the full flow, the SorbOx comes with high purity magnesium anodes and a demineralisation filter, depending on your needs, if you have an existing system that requires a little clean up, fit the demineralisation cartridge for a few days to clean up the water it will remove the salts and minerals from the circulating water, then swap for the magnesium anodes for ongoing protection


For larger systems up to small commercial there is the Trio range, The 10 for system volumes up to 500L, 15 for system volumes up to 1,500L & 25 for system volumes up to 5000L, these units can be fitted in the full flow or side stream, in side stream installation a flow setter should be installed and the correct flow rate needs to be set for the unit, these units provide three proven corrosion-protection measures, Degassing, Anodic Protection and magnetic protection, they have also released a new line which has the addition of a replaceable filter, so adding a fourth line of protection


For large commercial systems Elysator have the Elysator Industrial units, these units are installed as a sidestream, starting at the 50 for volumes up to 15m3, 75 for system volumes up to 25m3, 100 for system volumes up to 35m3, 260 for system volumes up to 70m3, 500 for system volumes up to 120m3 and the 800 for system volumes up to 220m3, the principle for 3 tier protection is the same for this unit and across all the range, Degassing, Anodic protection and magnetic protection 

Elysator Industrial

All the above items offer at least three levels of protection for the system water using Magnesium Anodes, so how do these work?

Within each of Elysator units which is where the reaction occurs, whether it's the SorbOx, Trio or Elysator Industrial units, we have the stainless steel body of the unit and the magnesium anodes inside, it is within the vessel that the exchange occurs so these units are classified as the the reaction vessels.

Magnesium is less stable than steel, so in an environment where corrosion factors are present, then the Magnesium will corrode (oxidise) first.

The more noble a metal is, the more resistant it is to corrosion when submerged in an electrolyte like water, as explained at the start, both stainless steel and magnesium have excess electrons which they want to give up to become more stable and here is where the difference in nobility becomes relevant, Stainless Steel as the more noble, has to take excess electrons from the magnesium even when it's looking to shed its own surplus electrons and is therefore protected from oxidisation, this process of the magnesium giving up its electrons (Oxidisation) (Anodic)  and the stainless steel taking these electrons (Reduction) (Cathodic) is a chemical reaction and combining the two reactions Magnesium ions and Hydroxy ions are formed within the water in the Elysator reaction vessel combining to form Magnesium Hydroxide
this Magnesium Hydroxide mostly remains within the reaction tank, so any water that passes through will react with the Magnesium Hydroxide which will raise the pH of the water, this is a gradual process and continues until the entire system water pH has been increased.

As stated previously, oxygen is the enemy of a heating system, the Elysator reaction vessel will consume dissolved oxygen present in the water that passes through it. As the magnesium anodes and the stainless steel tank are connected, the electrons from the magnesium move to the surface of the stainless steel tank, as stated earlier metals want to lose electrons to make themselves more stable and because stainless steel is a more noble metal the electrons from the magnesium move to the stainless steel walls of the Elysator Reaction vessel, now as opposed to metals that want to give up electrons to become more stable, oxygen wants to gain electrons to become more stable, so any dissolved oxygen in the system water will be drawn to the walls of the reaction vessel, as there is an abundance of electrons there, when the oxygen takes these electrons a chemical reduction reaction occurs O2 + 4e- + 2H2O → 4OH- this process consumes the Oxygen, from this hydroxy ions created on the the stainless steel and magnesium ions, created on the anodes combine and produce Magnesium Hydroxide, this is a solid, which drops to the bottom of the reaction vessel, this solid Magnesium Hydroxide will get dissolved into water with a low pH as it passes through the reaction vessel, so simply put, Elysator reaction vessels consumes the dissolved oxygen and uses it to increase the pH of the system water.

These processes within the reaction vessel of Elysators are a continuous process and continues as long  as there is oxygen to consume and pH to raise, once all oxygen has been consumed and all the system water pH has been raised the system is fully protected, but if for any reason oxygen gets back into the system or  pH variation occurs, as water passes through the Elysator reaction vessel the process will recommence and is how it continuously protects the system, always consuming oxygen and raising pH to levels suited to the heating system, it is Oxygen and low pH that are the main cause of corrosion within heating systems, so these methods will protect the heating system from these issues and so prevent corrosion.

I have installed many of these systems now and I know they work, I have cleaned up many district heating systems with these methods and have long term systems out there both domestic and commercial protected with these methods that are running clean and problem free, so this post is coming from an installer experience prospective and not sales  



Monday 20 January 2020

Filling a Heating System with Demineralised Water

Following on from my previous post I will now cover filling heating systems with demineralised water which is a requirement of VDI2035, this is a good and cost effective option for the domestic market here in the UK

The product I use controls the pH during filling to 8.5, this is ideal for heating systems, these units also remove salts, lime and TDS via the resin cartridge, so create water with low conductivity no scale deposits and correct pH for a heating system, this is essential in preventing corossion, water with low conductivity will restrict the path of corrosion, even in the presence of oxygen, although we don't want oxygen in our systems, it just shows that even with an oxygen ingress, the system can still be protected with the correct water, although I would always suggest any oxygen ingress needs to be found and eliminated

The unit I currently use is the Elysator Purotap Leader, these are great units, as an installer i take this from site to site with me and fill the system through the cartridge, as per the image at the header of this blog, the display on the Leader shows me the conductivity of the incoming water (figure on the right) and on the left it shows the conductivity of the water going into the heating system after it has passed through the cartridge, it also shows me the volume of water that has passed through the unit, so I know the exact fill volume, each cartridge will fill multiple systems, but how long the cartridge lasts will depend on the hardness of the water in the area you are in, obviously the higher the hardness of the water the sooner the cartridge will be depleted, but down here in the South East where we have very hard water, I get multiple fills, so very cost effective, but I have confidence knowing that the fill water of my systems has a pH of 8.5 and low conductivity, unlike with chucking in chemicals, I have no idea what the pH is and chemicals actually increase the conductivity of the water, I have been using these methods now for over 7 years, I know they work.

Using the Leader is simple, just connect the mains water supply to the inlet connection on the Leader and then connect the outlet of the Leader to the heating system connection, so basically it's just putting the leader in the line of the quick fill of a heating system, so rather than the raw mains been put straight into the system, the mains water goes via the Leader and the water is treated

Below is a image showing the Leader is connected for filling a system

Once the system has been filled, then the question often gets asked what about future topping up of the system, well this is covered by fitting a purotap micro, a small unit that gets fitted to the wall and connects to the quick fill, the cartridge in this unit ensures any top up water is treated so the water is also conditioned, keeping the water in the system at its optimum, but like anything the cartridge in the Micro will deplete, so during boiler service the condition needs to be checked and replaced if necessary, it is easy to identify when the cartridge is spent as it changes colour from Blue to a pale grey/beige colour

Below is an image of the Purotap Micro, which comes with a wall bracket for easy installation

 In my opinion this method of conditioning the heating system water is by far a better method, you are providing chemical free water which will prevent corrosion, I will continue to use this method to fill my systems and I actually see this growing amongst installers as they face water quality issues with longer boiler warranties, this method is used in Germany, Austria and Switzerland, they use the same makes as boilers as the UK, same pipe work and same heat emitters radiators or UFH, so something which i have heard mentioned before where some say this method is not suited to the UK is utter nonsense

I hope this helps explain how to use a demineralisation unit to fill a heating system and the benefits it provides in corrosion prevention, the next blog will be on the Elysator SorbOx

Sunday 19 January 2020

What is VDI2035

The VDI2035 are guidelines set by the Association of German Engineers, it is their method of water quality requirements for heating water, as a comparison its equivalent in the UK would be BS7593:2019 but the VDI2035 is way more in depth and scientific than the brief coverage BS7593 gives, there are also similar requirements in Austria H öNORM IN 5195-1 and in Switzerland SWKI BT 102-01, but what is common in all these standards is the non use of inhibitors.

There are 3 parts to the VDI2035 
Part 1 deals with Scale Formation in Drinking Water  and Water heating Systems
Part 2 deals with Water-Side Corrosion
Part 3 deals with Corrosion by Fuel Gases

So for my purpose of raising awareness in heating system corrosion we will only look at Part 1 & 2,.
I will not be going into full details, just an overview so installers can understand these standards and then we can question why these methods are not more widely used in the UK

Part 1 In brief Part 1 deals with the prevention of scaling within the heating system, to prevent scaling we need to ensure the hardness of the water is within certain levels to prevent scaling forming, this is measured in Total hardness in mol/m3 h and the levels permitted in the standard will be dependent on the Total Heating Power in kW (see my website link at the end for more details) using demineralised water will acheive this.

Part 2 In brief Part 2 For the prevention of corrosion in the heating systems the main points the VDI2035 document are concerned with are pH, Conductivity and Dissolved Oxygen, pH is stated to be between 8.2 and 10 these figures are the same across the regulations in Austria and Switzerland, however in the UK in the installation manual of some manufacturers we see the figure of between 6.5-8.5 why they would ever want a pH of 6.5 in a heating system this is acidic and would certainly lead to corrosion, I would never want a system with a pH of 6.5, to control the pH the use of filling units where the water passes through a cartridge of resin, this process will alter the pH of the fill water
For conductivity they look to have a level of  <100 µS/cm. the salinity and total dissolved solids in the mains water supply will determine the conductivity of the water, high conductivity of water allows the passage of corrosion a better route to cause corrosion in the presence of oxygen, so reducing this path by lowering the conductivity of the water significantly reduces the risk of corrosion even in the presence of oxygen
Dissolved Oxygen, Oxygen virtually always enters the system during filling procedures. This is because normal drinking water contains approx. 8-11 mg of dissolved oxygen per liter of water. However this quantity is generally used up (through corrosion processes) within a short period of time without significant damage occurring. However, oxygen can be harmful if it is able to consistently enter the system from the ambient air. This may occur due to a number of factors, such as partial formation of underpressure in the system, air entrapment during filling and top up procedures, direct contact between system water and outside air, and oxygen diffusion through permeable components such as seals, plastic pipes, diaphragms and hoses.

This is just an introduction to these standards and the alternative methods to controlling corrosion in our heating systems, both domestic and commercial, it's time we started asking questions as to why other major countries in Europe do not permit the use of chemicals in their heating systems (only permitted in exceptional circumstances) and yet here in the UK we are still told that chucking chemicals in will solve all heating system problems, but we know they do not, I personally have been in the industry 38 years and I see failure after failure of systems that have been inhibited as our British Standards guidance tell us to do, but as an industry we never question this, we just keep chucking chemicals in, why do we keep doing the same thing and hope for a different outcome, I think it's high time we had a grown up conversation on this subject, the industry needs to be made aware of the better alternatives to corrosion prevention that are available to us and we need to push for these methods to be stated in our regulations.

This is the first of a series of blogs I will be doing on this subject, I will also be covering the alternative options we have available to us for corrosion prevention, how to use them and what they do.

Further details on my website 

Tuesday 13 August 2019

Lead in Water

There has been mention of Lead in Water on social media, but we never seem to have a serious discussion about it, so I thought I would write a blog and see if we can generate discussion and take the matter more seriously.

The World Health Organisation (WHO)  and the European Chemicals Agency (ECHA) have now classified lead as a reproductive toxicity Cat 1a, a quote from the WHO website on lead

"Lead is a cumulative toxicant that affects multiple body systems and particularly harmful to children"

So as you can see, it's not a trivial matter, when the subject of lead solder use in plumbing is raised on social media I see lots of responses which trivialise the subject, people stating that they buy lead solder, or they always carry lead solder in their tool bag and try and warrant this by saying they only use it on gas or heating systems, well there are three issues here, firstly, having a role of lead solder in your tool bag means you have now contaminated your tools, this means lead is on your hands and everything you touch in a customers house could now be contaminated, I know this sounds extreme, but it's factually true, you are now risking the health of the occupants of that property
secondly, if you use lead solder for joints in a sealed heating system, the problem is now the water in that heating system is a toxic soup (as my colleague Paul Daley would call it) especially as this can be mixed with chemical inhibitors, this raises the heating water within that system from fluid category 3 where a double check valve will suffice for backflow protection for the quick fill to a fluid category 5, and this requires a much more complicated and expensive option for backflow protection, and thirdly, if lead solder is used on gas, often some of this pipe is exposed, so can be touched by the people whose property it is, including children, so again, they can be contaminated.

Why use lead solder at all, for me I don't understand why it is even permitted for sale now in the UK, I personally have not used leaded solder since around 2001, I used lead free solder for all my joints, whether that was heating, gas or water supplies and since around 2003 I moved to press fittings, so in my personal opinion there is absolutely no need for lead solder in our industry.

Now I know there will be some who are thinking, I am been a bit OTT with how harmful touching lead solder joints, or contaminating tools with a roll of solder in your tool bag, but just to prove how a minimal amount of lead solder in joints can affect the water supply, have a read of this case study from WRAS just see how much the lead content of the water was raised by just 5-6 lead soldered joints, this shows the dangers of lead solder and how high lead levels can go with such a small amount of lead in contact with the water, way higher than recommended safe levels.

I just feel we need to start having a sensible grown up conversation on this subject, I do not profess to be the expert in this matter, I gained my knowledge on this issue from Simon Reddy and Paul Daley (Captain Backflow) who have much more knowledge than me on this subject.

Water Regulations

The Water Regulations came into force in England and Wales in 1999 and the Scottish Water Byelaws were also updated in 1999 but differ slightly from England and Wales Regulations.

Water quality for safe drinking water for the public is highly important, however, I feel that the Water Regulations are not pushed as much as they should, I personally think this is due to so much focus been placed on Gas and the Gas Regulations, that installers have let their attention slip a bit on Water Regulations and this includes me.

Let's look at one of the most flouted regulations in my opinion, WC fill valves, most properties are now either on unvented cylinders and Combi boilers, this means the cold water to these properties are fed from the water mains, I understand that some properties are still tank fed and if the tank supply is feeding the WC this is fine and the following scenario will not affect these installations, but if the WC is fed from the mains and the customer calls a plumber in as their WC is overflowing continuously, on inspection the plumber decides repair is not an economic solution, so decides to replace the ball valve, he goes to his van and takes out a brand new valve, these new ball valves are quick to fit and give options to adjust height to suit the WC cistern and most importantly they have WRAS approved on the box, the plumber fits the new ball valve, all works well and the customer is happy as they have a nice quiet fill valve that does not overflow, the plumber is happy he has done a good job and feels he has complied with the Water Regulations as he has fitted a WRAS approved ball valve, but unfortunately the plumber has broken the water regulations. I have done this and I found out when I posted a picture on Social Media of a replacement ball valve I had installed, when a good colleague of mine Paul Daley (Captain Backflow) contacted me and told me that the type of ball valve I fitted requires a double check valve to be compliant, I said no it's OK the ball valve is WRAS approved, not quite was his reply.

The problem with WC fill valve manufacturers putting WRAS approved on the box is not the whole picture and is misleading in my opinion, when you go to the WRAS website site  and look up the particular fill valve you have, it will most likely be WRAS approved and have an approval No for that particular product, however, it will come with IRN these are Installation Requirements or Notes, nether the IRN No or its contents are mentioned on the box of the fill valve, or in the installation instructions, however, without adhering to these IRN's from WRAS the product will be contrevening the Water Regulations, as it is not fully WRAS approved without complying with the IRN, but the onus will be on the installers, for example and not mentioning any products, one of the IRN that are on a well known WC fill valve brand is IRN R160 this states the following

"A Compliant double check valve or some other no less effective device providing backflow prevention protection to at least fluid category three shall be fitted at the point of connection(s) between the water supply and the fitting or appliance"

It also has IRN R280 which states,
"A service Valve shall be installed on the supply to the fitting in a readily accessible location"

And also IRN R390 which states,
"An inlet strainer or line strainer shall be provided at the inlet"

NOTE: Not all fill valves require a strainer, but most of the new types of fill valves do require a check valve, usually single for side inlet and double for bottom inlet

Now, without fitting these additional components, the fill valve is NOT WRAS approved and is in contravention of the Water Regulations, I have only highlighted one risk that mostly gets ignored there are more, including the fitting of kitchen sink taps with the pull out hoses that can go below the waterline of the sink, which is a fluid category 5 risk and so check valves are insufficient for protection, the fitting of hand held shower hoses at WC used for washing after WC use, again a category 5 risk, but plumbers fit them with double check valves thinking that is sufficient protection and I am sure there are many other regulations that plumbers are contrevening without even realising it, I think we need to draw more attention back to Water Regulations, improve our knowledge more on the regulations, but I do feel that Water Safe and WRAS can do more to highlight these risks, also we need more updates on Regulation changes etc, it's time we took our drinking water protection more seriously as plumbers, I urge all plumbers to join either Water Safe or WIAPS, let us all work together.

These schemes are free to join, as long as you have a formal plumbing qualification, have taken the Water Regulations course and have public liability insurance, it is down to us plumbers to raise awareness, share knowledge and improve our industry, if we wait for others, it will never happen

Wednesday 31 July 2019

PAS2035 will this be forced upon all boiler changes

Most might of seen the recent articles regarding PAS2035 this has been brought in for Government eco grant system projects, but what is it, well in my personal opinion it's just unnecessary bureaucracy, all it does is create more people in line who want money from a simple boiler change for doing very little to nothing, I see no benefits to either the installer or the homeowner in this PAS2035, in fact the installer probably comes off worse, as the cream has been taking as it passes through the chain and very little is left for the essential part of the job, the actual installation of the boiler, now I am not involved in this eco work but from others I have spoken to who end up either servicing or repairing boilers that were installed under eco scheme, they say the installation is not of a very good standard, this is probably because the installer does not have the money in place to do a good job, in my opinion and that of many other installers, to do a good job on a boiler change, it often takes more than one day, if all works are carried out properly.

So I suppose you're wondering, well, if you don't do eco work, why should PAS2035 concern you?, well my problem is, I see this creeping into all boiler changes at some point and I think this is their aim,  I would see this as a disaster for our industry.

Where has PAS2035 come from, its from a bunch of certification bodies, so not industry, and why would they do this, well in my opinion, its money, nothing more, I see no benefit to anyone, maybe they could try and explain to us installers how it would benefit anyone, homeowner or installers, from another article I have seen the figure of 6,000 boilers a day are replaced in the UK, now most of these are handled by sole traders and SME's I should imagine, and the majority are dealt with quickly and if the boiler exchange was a a distress change, where the boiler has broken down and not repairable, its changed quickly, so the customer is least inconvenienced and has their heating back on, with this PAS2035 the process would take much longer, so leaving homeowners cold

As an installer , I don't want this creeping in to our everyday jobs changing boilers and with conversations with other installers no one else does, we must nip this in the bud before they even consider extending this scheme, so we need to stand together as an industry and say, enough is enough, our industry has been milked for far to long.

What we need to do is contact our local MP's and let them know we will not except this infringement on our ability to work, a contact on Twitter has said they will share a template letter that installers can use to send to their MP, as soon as I have this I will add it here, I just thought I would get the word out ASAP so we can start spreading the message, just so you know I am not just making this up, here is a recent article about it in Installer magazine

So let's start a discussion and get the message out to as many installers as possible, we need at least 10,000 installers to contact their MP to show we are not happy about this

You can find your local MP HERE and isa link to a template letter to your MP should you wish to use it can be found HERE

Thank You for Reading

Monday 15 July 2019

Water Treatment

As most of you are aware I am not a fan of chemicals been used in heating systems, we have other options, these options are widely used in Europe, yet the UK chooses to ignore these proven methods and continue to push the chemical option.

We had an interesting conversation on Twitter regarding water treatment, but what I realised is many UK installers are unaware of the alternative options, so i thought I would share the different methods available, these follow the German VDI2035 methods

Softened Water
Some people have mentioned using softened water to fill a heating system, here are the fact on this.

By softening of filling water via ion-exchange the total hardness of the heating system make-up water is reduced.

By removing calcium and magnesium out of the water the total hardness is lowered. This basically comes up to the demands according to VDI2035 guidelines. But replacing calcium and magnesium against sodium ions does not lower the electrical conductivity of the heating water. In most cases the electrical conductivity of the softened water rises due to technical reasons in comparison with the untreated raw water.
This critical factor makes softened water unsuitable for heating-system make-up water, if there is a higher amount of oxygen to be expected in the heating system there would be need for water with a conductivity of <100 µS/cm.
In systems with higher temperatures, a high pH above 10 may occur, if the system has been filled with softened water. As the sodium has exchanged its position with calcium it is dissolved in the water in form of sodium-hydrogen carbonate – its partner in solution is carbon dioxide. As soon as the water is heated up above 60°C, the solubility of gases in the water is lowered and carbon dioxide changes from the aqueous to the gaseous phase. Sodium stays in the water mainly in form of sodium hydroxide which might results in a pH >10.
Due to these technical based restrictions a filling water treatment with water softening does not cover all demands of the common guidelines for heating water treatment.

The de-ionisation by ion-exchange follows the same principle as water softening, but the de-ionisation of the heating-system filling water lowers the electrical conductivity and the total hardness.
At the process of de-ionisation the ion-exchanger consists of two components – the cation- and the anion-exchanger.
The difference to water softening is the cation exchanger is not loaded with sodium-salts, but with hydrogen-ions. As soon as water comes in contact with the cation exchanger all positive charged ions (potassium, sodium, calcium, magnesium) change their position with hydrogen-ions.
The anion-exchanger is loaded with hydronium-ions. These swap their position with any negative charged ions in the water (carbon dioxide, silica, chlorides, sulphates, nitrates).
The treated water thus contains H+ and OH- ions – ions where water molecules are made from. The H+ and OH- ions combine to H2O – pure water.
The de-ionisation of heating-system make-up water generates a water, which has a low electrical conductivity of <10 µS/cm, a total hardness of ~0,1°dH and a neutral pH of ~7-8. All salts, even chlorides, sulphates and nitrates are completely removed from the water.
But with this ion-exchange principle, the pH can cause problems. Improper use of the ion-exchanger salts of silica and carbon dioxide are not removed properly. As a result the pH of the treated water drops and the water becomes slightly acidic with a pH of 4-5. Even correct use of de-ionisation the pH can drop as soon as there is an acidic reaction in the system. De-ionised water is rather sensitive to outside influences as there are no dissolved salts that can act as a buffer against such influences.
In ordinary heating-systems without disturbing impurities and without constructive deficiency the pH of the de-ionised water normally rises to approx. 8.2 after one or two weeks of operation. This assumes that the water is heated up to >60°C and that the system is de-aerated properly so that residues of carbon dioxide can be vented. This and some metal hydroxides results in a rise of the pH.

Demineralisation with pH control
There are also water filter system available, for the reduction of total hardness and electrical conductivity as well as stabilisation of the pH of the heating system water.
The pH is raised by constant dosing of suitable salts. In the first stage in the chamber the water is adjusted to a specific level by use of a special resin. In a second filter stage suitable salts are dosed to the water depending on the volume flow, which results in a rise of the pH. By use of a special salt-resin mixture the pH can be limited. The result is a water with an electrical conductivity of 1-100 µS/cm, a total hardness of ~0.01°dH and a pH of 8.5. Regardless of the raw water quality such filters create water that fully complies to the demands of VDI2035 guidelines for heating-system water quality. Products which provides such water treatment are the CLARIMAX 1200 HW water filter system and the Elysator Purotap Leader with the Nexion cartridge.

Electrochemical solutions
The use of electrochemical water-treatment will results in an increase of the pH-value, constant oxygen consumption and cleaning of the system water. A cyclonic water flow and separation plates installed inside of the unit enhance the separation of impurities and the venting of the heating system by an air-vent. In addition, a strong magnetic filter rod of rare-earth provides the effective removal of magnetic particles from the heating water. Protection of the metals in the system by a water quality which supports the formation of natural protective layers and passivation (corrosion protection) The electrochemical water treatment is a well known method for an eco-logical corrosion protection in central heating systems and is a recommended method for refurbishment and protection of central heating systems in the case of water containing oxygen resulting in corrosion.  The increase of the pH-value by electrochemically formed hydroxide is state of the art technology and a safe way to operate a central heating in combination with demineralised water in a low-salt operation style according to VDI 2035. these units come in varying sizes and are particularly useful in large commercial systems suffering from corossion, as they can be fitted into the system with minimum of disruption and will treat the water over time, bringing it to a clean and non corrosive condition

System Top Up
If these methods are used its important to use conditioned water for any top ups, cartridges are available that can be connected to the quick fill of the heating system, which ensure any top up water is the same quality water that you filled the system with.
There is much more to this, but I have tried to keep it as brief as possible