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Technical Information

What Combiphos does

What do Combiphos crystals do to the water?

As mains water passes through the Combimate unit it flows through the Combiphos crystals.

The calcium within the water attracts the phosphate within the Combiphos crystals – in so doing, the minerals are kept in suspension as the water flows through the hot water system, preventing the calcium sticking to hot surfaces and leaving a deposit of limescale.

Combiphos also coats the inside of the pipework, boiler heat exchanger and appliances with a non-residual, microscopic, protective coating. This again prevents scale-causing minerals from accumulating and aggressive softwater from corroding the system and appliances.

The action of the Combiphos does not soften the water but retains the health benefits of the natural minerals contained in hard water.

Pipes with Combiphos
Pipes with Combiphos
Pipes without Combiphos, heavily corroded by softwater
Pipes without Combiphos, heavily corroded by softwater

Scientific description

Above is a general outline of how the Combiphos process works – what follows is a more detailed description:

Two key processes occur that makes phosphate dosing effective as a water treatment.


The phosphate in Combiphos acts as a ‘chelating agent’. This agent has a binding (or ‘sequestering’) effect, reacting with the soluble metals (principally calcium, but also magnesium, iron, manganese etc)  in the water to form a ‘chelate’ (a compound) . By forming this compound, the metals maintain their solubility in water. Due to this action, calcium build up (limescale) is prevented from forming.

This phosphate sequestering process minimizes the risk of discoloration, staining, scaling, taste/odor and other water quality complaints


Very small dissolved particles within the water (those less than 10 microns in size) tend to bind to one another; attracted by regions of positive and negative charges on each particle. This clumping effect (known as flocculation) forms hard deposits out of a water solution and is at the heart of scale formation.

Combiphos prevents this process by coating the small particles in phosphates; reducing their attraction to one another. These ‘deflocculated’ particles remain suspended in water, again reducing the opportunity for scale to build up.

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Combimate will last a lifetime and is virtually maintenance free.

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Combiphos refills

To maintain your Combimate’s effectiveness, we recommend Combiphos is replaced annually.


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