Limescale or deposits of scale can lead to reduced heat generator efficiency, cracking due to localised overheating and functional impairment of fittings. Limescale usually occurs where temperatures in the circuit are high, affecting boiler walls in particular.

ENEV has raised awareness of energy-saving operations of heating systems, thereby changing the guidelines on energy-saving and damage-minimising operation of heating boilers. The newly modified VDI 2035 Part 1 now requires that measures are taken to prevent limescale deposits in heating circuits, including heating systems lower than 50 kW.

Measures must be taken whenever regional water hardness exceeds the value in the table below. If the specific system volume per kW boiler output is >20 l/kW, the next higher group is to be used. If 50 l/kW are exceeded, softening to ~ 0°dH is generally required.

Softening is the surest way to prevent limescale formation, because softening removes the calcium that forms limescale. Softening by means of ion exchange resin is also a recognised technology and has been tried and tested millions of times over. Water with Ca and Mg ions is passed over a plastic resin containing Na ions thereby replacing the Ca and Mg ions with Na ions.

Alternatives to softening are: hardness stabilisation, hardness precipitation, physical water treatment and complete demineralisation. Hardness stabilisation and precipitation is achieved by adding phosphates or other chemical agents. However, the procedure has the risk of under- or overdosing. Physical water treatment uses magnetic fields to form lime crystals, which should not create any hard surfaces. The effectiveness of this procedure has not yet been convincingly proven. Complete demineralisation removes all salts (Mg, Ca, Na...) from the water and thus also eliminates the calcium (Ca) problem. However, pH values are changed by demineralisation, so that the water must be neutralised with alkaline agents (i.e. high technical costs).

Reflex Fillsoft is a simply designed ion exchanger that softens the filling and make-up water for heating systems. A cartridge filter housing is fitted with a cartridge filled with ion exchange resin. Fillsoft is installed behind the system separator (e.g. Fillset). The cartridge filter is used for initial filling and refilling. Soft water flows into the heating system. A water meter registers the amount of soft water extracted and indicates to the operator when it is time to replace the cartridge. The used cartridge is disposed of with household waste and a new cartridge is inserted.

Initial filling for systems with a volumes of up to approx. 1500 l can be carried out using 'Fillsoft'. Depending on the level of hardness, an additional number of cartridges may be needed for initial filling (see operating instructions).

Softening by ion exchange replaces calcium ions with Na ions in the water, meaning Fillsoft will not alter salt content and therefore also not the electrical conductivity. Softened water also does not increase the water’s corrosiveness.

New cartridges are relatively inexpensive, so regeneration is not worthwhile. Logistics costs (shipping, external regeneration, packaging) would exceed the cost of a new cartridge. Used cartridges can be simply disposed of with household waste.

Already softened water will become hard again if it is left in the ion exchanger for a longer period of time. For this reason, cartridges with a minimum water content are being used, so that even if the make-up water is left in 'Fillsoft' for longer periods of time, only the smallest 'hard' quantities of water will be introduced into the system.

Conventional softening is achieved using Na ion exchangers. In the process, hardness-forming Ca and Mg ions are replaced with Na ions. The water's chemistry is not interfered with in any other way. Electrical conductivity and ph-values remain unchanged, so that no extra water conditioning measures are required.

H+ ion exchangers are also available which exchange the cations (calcium and magnesium) for hydrogen ions rather than sodium ions. Hydrogen ions lead to an increase in hydrogen protons and thus inevitably (see definition of ph-value) to a shift of the ph-value into the acidic range. Adding alkaline additives is imperative here.

Decarbonisation uses the ion exchange principle to remove carbonate hardness (i.e. the hardness that occurs as limescale in the heating system) and hydrogen carbonate (HCO3-) from drinking water. Since hydrogen carbonate is the main determinant (i.e. how strongly low acid or base additions affect the pH value) in water buffer systems, the removal of hydrogen carbonate is usually associated with other water conditioning measures.

Complete demineralisation
Complete demineralisation carried out by a mixed bed ion exchanger will have adequate effects according to the above. The water is passed over a strongly acidic and strongly basic ion resin, which filters out the cations (Ca, Na, Mg; etc.) and anions (Cl, HCO3, etc.) and exchanges them for H+ and OH- ions. Hydrogen carbonate (in the anion exchanger) is also removed from the water, which means it lacks the buffering effect against acid/base influences. Further treatment is therefore essential after complete demineralisation. Complete demineralisation has the advantage of removing all salts, so that electrical conductivity tends towards zero. Higher oxygen contents in heating water can then be tolerated. However, no standard or directive requires full demineralisation in heating systems.

In the sodium ion exchanger, which is also used in 'Fillsoft', the cations (Ca and Mg) are replaced by Na. As a result, salt content remains unchanged, but also the pH value is unaltered, so that no additional measures for neutralisation – due to softening – need to be carried out. From the Buderus heating technology manual (2002 edition)

The frequently held view that softened water (note: by means of a sodium ion exchanger) requires further treatment with chemicals because of its alleged “aggressiveness” is not well-founded.

According to the equation Ca

(HCO3)2 CaCO3 + CO2 +H20,

limescale (calcium carbonate) occurs when the calcium hydrogen carbonate decomposes into calcium carbonate, carbon dioxide and water by heating the water. The calcium carbonate forms hard deposits in the form of scale and gas is removed from the system, e.g. via automatic quick ventilators.

There has been an increased risk of scale formation since the introduction of the ENEV and the simultaneous development of heating technology towards more compact heat transfer surfaces. The trend towards multiple boiler systems also means that small boiler units have to temporarily take over the heating of large system volumes. This increases the risk of scale formation on components with very high temperatures.

Pipelines are also at risk from limescale deposits, which over time significantly reduce their diameter, increasing pressure losses and pump energy consumption. As a result of system heating and deheating processes, limescale particles become detached from linings and can lead to problems with control valves, safety valves or pumps.

For this reason, the current VDI Guideline 2035 Part 1 has significantly tightened the requirements for preventing scale formation and already requires appropriate measures for a “20 kW boiler” when regional water hardness exceeds 16.8 °dH.

Because household budgets are getting tighter and tighter, the energy-saving aspect alone should be incentive enough to install a softening system. 1 mm of scale on boiler walls causes an approx. 10% drop in efficiency. So with an annual heating bill of €1,000, the use of a 'Fillsoft' will quickly pay for itself. The soft water also causes already formed scale deposits to dissolve until a balance of lime and carbonic acid is achieved. The potential warranty claims against boiler manufacturers are easier to enforce with the use of treated water (according to VDI 2035) than without it, especially since today every boiler documentation requires that this guideline be observed and implemented.

FAQ Sinus buffer tanks

One way to determine tank volume is to use dimensioning that minimises pulse frequency*.
When using solid fuel boilers, tank volumes must be determined according to the specified heat output. This is because fuel input cannot be managed as flexibly for solid fuel boilers as, for example, for oil or gas.

*Pulse frequency: Pulse frequency is the time between switching off and restarting the heat or cold generator.

The following data is relevant for dimensioning:

  • Thermal capacity (heating or cooling capacity)
  • Storage time
  • Temperature spread between flow and return
  • Max. diameter
  • Max. height / tilted dimension
  • Configuration pressure
  • Configuration temperature
  • For solid fuel boilers, boiler output and combustion period* is required.

*Combustion period: Combustion period is the length of time taken for a solid combustible to burn.

Specifications and parameters for a buffer tank can usually be obtained from the planner or system builder. If this is not possible, the manufacturer of the heat generator or cold water system can also provide the information.

FAQ Sinus ProfiFixx

Unfortunately, the table data is not available in this language.

Kompaktverteiler HydroFixx
Typ FB-OK-Dämmung
Typ FB-OK-Dämmung
160/80 1.865 mm 160/160 1.960 mm
180/110 1.905 mm 180/180 2.000 mm
200/120 1.905 mm 200/200 2.000 mm
280/180 1.990 mm 280/320 2.150 mm
300/200 1.990 mm 300/500 2.150 mm


The centre–centre width from pump group to pump group is 620 mm

Unfortunately, the table data is not available in this language.

Pumpengruppe Mischerbezeichnung Anschluss kvs-Wert
ProfiFixx DN 25 VRG 131 20-4 3/4" Innengewinde 4,0 (2,5 und 6,3 auf Anfrage)
ProfiFixx DN 32 VRG 131 25-10 1" Innengewinde 10,0 (6,3 auf Anfrage)
ProfiFixx DN 40 VRG 131 32-16 1 1/4" Innengewinde 16,0
ProfiFixx DN 50 VRG 131 40-25 1 1/2" Innengewinde 25,0
ProfiFixx DN 65 VRG 131 50-40 2" Innengewinde 40,0
ProfiFixx DN 80 HFE 3 DN 50 Flansch 50/6 60,0

Yes, these can be installed vertically (at a given height) or horizontally (see drawing) in the connecting pipelines.

Diagram showing “Heat meter at the supply
Diagram showing “Heat meter at the ProfiFixx

Yes. It can be placed in the supply.
An Exdirt V can be used in the supply group as an alternative to a dirt trap in each heating circuit.

The three-way mixing valves of the controlled heating circuits are compatible with virtually any control units from regular manufacturers. For further technical information, please contact our technical support:

Christoph Storm
+49 (0)2557 / 9393-47

Yes, additional sensor sleeves can be fitted. Ideally, these are mounted outside the insulation box so as not to impair insulation properties.

The pump groups are equipped with two additional (1x VL 1x RL) ½" sleeves, which can optionally be used for immersion sleeves or similar.

FAQ Sinus HydroFixx

Yes. Differential pressures can be compensated and mass flows can be equalised. Compared to a conventional construction method, HydroFixx also offers material, assembly time and space savings.

Several heat generators can be connected. These are to be arranged in a row. They must not be connected randomly to the HydroFixx. When combining heat generators with different flow temperatures, ensure that the connection with the lowest flow temperature is positioned closest to the system side.

Primary connectors can be arranged in both directions. Their connections are each arranged with a connector on the left and a connector on the right towards the head end.
The secondary connectors, on the other hand, must generally be installed in one direction, i.e. pointing upwards or downwards on one side.
The supply connections may also be positioned as a connector pair on the outside left or right of the manifold end – towards the heating circuits. Several primary points next to each other are also possible in this order. A central connection from the heat generator to the HydroFixx is only possible under certain conditions and requires consultation with the factory. This also applies to the functionality of a connector at the head end.
The order of the connectors can be varied. A constant change between flow and return is not mandatory.

The sensor sleeve for flow temperature detection is always installed so that the sum of all volume flows of the heat generators and the transition to the hydraulic separator can be detected.

FAQ Sinus hydraulic separators

The essential function of hydraulic separators is to hydraulically decouple boiler and consumer circuits from each other.

Hydraulic separators are the optimal solution for avoiding hydraulic faulty switching, especially when flow rates are different for heat consumers and heat generators. The use of hydraulic separators also prevents mutual interference between primary and secondary pumps or control valves.

In most cases, temperature is measured at the secondary flow, as this supplies the heating circuits and also has to provide the necessary amount of energy with mixed return water. This ensures that it is not just the boiler flow temperature that is measured, but the mixed water temperature from the boiler flow temperature and the mixed return temperature that goes to the system in bypass mode. This is the most common type of regulation. However, there are certain cases where the return temperature must also be taken into account. The sensor for measuring flow temperatures is therefore normally located in the core flow to the system; in special cases, the sensor position should be discussed with the manufacturer of the boiler or control system.

The Hydrofixx can be used in almost any system where a hydraulic separator is required, provided that the hydraulic separator is located directly below the manifold and that no additional separator is installed.

Probably more than ever. Pump and control technology is improving all the time and there are currently many ways to hydraulically balance a heating system, but it is never possible to assess the behaviour one hundred percent at all times and in every operating situation.

Also, the amount of water in current-day boilers is sometimes so low that a hydraulic separator should be used to prevent the system from pulsing or even “running dry”.

The essential function of the hydraulic separator in heating systems is to hydraulically decouple boiler and consumer circuits from each other. Hydraulic separators are the optimal solution for eliminating faulty switching, especially, when flow rates are different for heat consumers and heat generators.

Vertically installed hydraulic separators produce temperature stratification due to the differences in temperatures and densities. This state persists for as long as no (serious) admixture takes place. In heating systems, this situation only really occurs in full-load operation.

Nowadays, when condensing boilers are used, part of the return water is generally added to the secondary flow to keep the boiler return temperature low so as to utilise the condensation effect. Hydraulic separators are therefore always operated in bypass mode, which prevents thermal stratification from occurring. This is why it is no longer necessary to position hydraulic separators vertically, as forces (buoyancy and gravitational) cannot act against the flow force because of the admixture.

The larger of the two (primary or secondary) volume flows at full load must always be used for dimensioning.

The result of this maximum volume flow at a speed of <0.2m/s defines the separator’s cross-sectional area and from this the diameter can be derived. The velocities in the connectors should be around 0.7 to 1.2 m/s (according to the size), depending on the pipe calculation. The height of the separator is defined by the distance between the primary and secondary connectors, which should be at least 2.5 times the diameter, or 10 times the nominal connection diameter in the low power range.