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3.4
Water quality
3.4.1
Quality requirements for the heating water
The quality of the fill and top-up water is an essential factor for increased
efficiency, functional reliability, long service life and for maintaining the
operational readiness of a heating system.
Unsuitable water can damage the heat exchanger or cause a fault in the
heat generator or DHW supply!
Unsuitable or contaminated water can lead to sludge formation,
corrosion or scaling. Unsuitable antifreeze or hot water additives
(inhibitors or anti-corrosion agents) can damage the heat generator and
heating system.
▶ Only fill the heating system with potable water. Do not use well or
groundwater.
▶ Determine the water hardness of the filling water, before filling the
system.
▶ Flush the heating system prior to filling.
▶ If magnetite (iron oxide) is present, anti-corrosion measures are
required and the installation of a magnetite separator and a de-airing
valve in the heating system is recommended.
▶ The limit values in table 3 must not be exceeded, even if national
directives contain higher limits.
Water quality
Unit
Conductivity
μS/cm
pH
Chloride
ppm
Sulphate
ppm
Sodium
ppm
Table 3 Boundary conditions for potable water (filling water)
▶ Check the pH value after > 3 months of operation. Ideally at the first
service.
Material of heat
Heating water
generator
Copper brazed
•Untreated potable water
heat exchangers
•Fully softened water
• Low-salt operation < 100 μS/
cm
1) If pH value is < 8.2 an on-site test for ferrous corrosion is necessary
Table 4 pH value ranges after > 3 months of operation
▶ Treat the fill and top up water according to the instructions in the
following section.
Depending on the hardness of the filling water, the system water volume
and the maximum heat output of the heat generator, water treatment
may be required to avoid a damage in water heating installations, due to
the formation of lime scale.
AW 4 | 5 | 7 OR-S – 6721866761 (2023/06)
Requirements on the fill and top-up water
y
Fig. 16 Heat generators < 50 kW-100 kW
[x]
[y]
[1]
[2]
Value
≤ 2500
≥ 6,5... ≤ 9,5
For systems with a specific system water content >40 l/kW, water
treatment is mandatory. If there are several heat generators in the
≤ 250
heating system, then the system water volume must be related to the
≤ 250
heat generator with the lowest output.
≤ 200
1°dH=
pH value range
1°e=
1°fH=
1)
7.5
– 10.0
1 ppm
CaCO3
1)
7.0
– 10.0
(USA)
1mmol/l=
Table 5 Water hardness unit conversion
A recommended and approved method for water treatment is
desalination of the fill and top-up water to a conductivity of ≤ 10 μS/cm.
Prevention of corrosion
In most cases, corrosion plays only a minor role in heating systems. A
precondition for this is however, that the system is a corrosion-sealed
water heating installation. This means that there is practically no access
of oxygen to the system during operation.
Continuous introduction of oxygen leads to corrosion and can thus cause
rusting and rust sludge formation. Sludge formation can not only cause
blockages and therefore a diminished heat supply but also deposits
(similar to lime scale deposits) on the hot surfaces of the heat exchanger.
The amount of oxygen introduced by the fill- and top-up water are
generally very small and can therefore be ignored.
To avoid oxygenation, connection pipes must be diffusion-tight!
The use of rubber hoses should be avoided.
The intended connection accessories should be used in the installation.
During operation, pressure maintenance with regard to oxygen ingress
and in particular the function, correct sizing and correct setting (pre-
3,00
2,80
< 100 kW
2,60
< 50 kW
2,40
2,20
2,00
1,80
1,60
1,40
1,20
1,00
0,80
2
0,60
0,40
0,20
0,00
0
5
10
x
Total hardness in °dH
Maximum possible water volume over the service life of the heat
3
source in m
Above the curve, only use desalinated fill and top-up water, with a
conductivity of ≤ 10 μS/cm
Below the curve, untreated fill and top-up water according to
drinking water regulation can be used
Water hardness unit conversion
°dH
°e
1
1,25
0,798
1
0,56
0,7
0,056
0,07
5,6
7,02
Preparing for installation
1
15
20
25
30
0010048707-001
°fH
ppm
mmol/l
1,8
17,8
0,1783
1,4
14,3
0,142
1
10
0,1
0,1
1
0,01
10
100
1
9
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