Heating water treatment to VDI 2035: fill with demineralised water and protect the circuit
Heating water treatment brings together the units that prepare the fill water and regulate the circuit water to prevent lime, corrosion and sludge in boilers, heat pumps and underfloor heating. Q-Tech gathers here the brands it sells to meet the VDI 2035 guideline. For all units, ask for a quote on WhatsApp.
How to choose between magnetic, ROTHENBERGER and SYR
Q-Tech has selected the brands in this collection on technical criteria and for the good results obtained in our installations.
We suggest looking at magnetic if you top up often and want to check conductivity with a meter, or if you also need to regulate the circuit water in operation; ROTHENBERGER, if you fill occasionally or top up during maintenance and prefer a compact cartridge in three sizes, with up to 10 litres per minute on M and L; SYR, if you want a fixed station that fills the heating system with treated water and a BA separator to DIN EN 1717 (built into the AC All-in-One 3228), with app control on the Connect versions and 2.5 to 14-litre cartridges refilled with granulate.
| Filling | magnetic | ROTHENBERGER | SYR |
|---|---|---|---|
| Capacity at 1 °dH | 3,000 to 48,000 l | 2,000 to 7,000 l | 2,185 to 50,960 l |
| Maximum water temperature | 60 °C | 60 °C for short periods | Not published by SYR |
| Maximum pressure | 6 bar | 4 bar for short periods | Not published by SYR |
| Connection | G ¾ | ¾" | Not published by SYR |
Summary for information purposes only, prepared by Q-Tech in November 2026 from the technical data sheets each manufacturer publishes, to help you get your bearings among the brands we sell. It is general and indicative: manufacturers update their data and a summary may contain errors, so each product page and the manufacturer's documentation always prevail, without prejudice to your rights as a consumer (Legal Notice). It is common for customers to change their mind once they know each brand's strengths, or to find that a feature they liked is not essential in their case.
A water treatment unit protects your system for many years, and a choice that does not fit your installation shows up in running costs and in wear on the boiler or heat pump. If you want to decide with the data of your own case, you can book our professional technical advice (a paid service): an Expert Technician reviews the features of your home and installation with you and guides you with Q-Tech's experience, under an obligation of means (Legal Notice).
Models in the collection
| Product | Function | Capacity |
|---|---|---|
| magnetic | ||
| magnetic NF plus | Permanent refill station with conductivity meter | 4,500 to 48,000 l at 1 °dH |
| Demineralisation cartridge 300 | Fills and small top-ups with colour indicator | 3,000 l at 1 °dH |
| magnetic HWR compact plus | Regulator for diffusion-tight systems | Up to 500 l of system water |
| magnetic HWR plus 10, 15 and 25 | Regulator with anode indicator | Up to 5,000 l of system water |
| magnetic HWR plus 50 and 100 | Bypass regulator with connection kit | Up to 35,000 l of system water |
| ROTHENBERGER | ||
| ROTHENBERGER PURE H2O | Demineralisation cartridge in sizes S, M and L and wall set | 2,000 to 7,000 l at 1 °dH |
| SYR | ||
| SYR AC 3200 | Fixed filling station with cartridge; separate FüllCombi BA separator | Depends on the cartridge |
| SYR AC All-in-One 3228 | Fixed filling station with cartridge and built-in FüllCombi BA | Depends on the cartridge |
| Pre-filled SYR cartridge | Softening (HWE), demineralisation (HVE) or demineralisation with stable pH (HVE Plus), 2.5 to 14 l | 2,185 to 50,960 l at 1 °dH |
| SYR replacement granulate | Refill for the cartridge of the same type | Depends on the cartridge |
Data according to each manufacturer.
How to choose the unit
- Fill or regulate: fill water is prepared with a station or a cartridge; circuit water is protected with an HWR regulator if oxygen gets in, for example with plastic-pipe underfloor heating.
- First fill: Q-Tech recommends doing it, where possible, with the magnetic demineralisation cartridge.
- Litres: divide the capacity at 1 °dH by your water hardness; the system volume and litres per kW come from our VDI 2035 calculator.
- Existing system: analyse the circuit water first; depending on the result, it is filtered in bypass without draining, or cleaned and refilled.
Applications
- Heat pumps with buffer tank and underfloor heating.
- Boilers and building plant rooms.
- Refurbishment of systems with sludge and corrosion.
Why choose Q-Tech?
- We integrate water treatment into the pre-assembled plant room, tested in our workshop.
- In existing systems, we offer the initial circuit cleaning through a partner company, or supply the filters and cleaning recommendations.
- We connect the unit with the on-site Expert Technician and explain the guideline values in our article VDI 2035: water quality in heat pumps and heating systems.
Frequently asked questions
What is the price?
Ask for a quote: message us on WhatsApp with the model and we will send it to you.
What do I need, filling or regulating?
It depends on the condition of the water. We recommend a laboratory analysis of the circuit water; if it is very poor, the system is drained, the circuit cleaned and refilled with demineralised water; if it is acceptable, solids are filtered out in bypass without draining and the water is protected with a regulator.
When does VDI 2035 call for demineralised water?
From 40 litres per kW, at any output; a system with a buffer tank and underfloor heating reaches it easily.
Ask for a quote for heating water to VDI 2035 or see more units in Climate Control.
Updated 07-11-2026 · v5.4