Prevention Of Damage Due To Corrosion On The Water Side; Using Antifreeze In Boilers - Viessmann Vitoplex 100 PV1 Service Instructions Manual

Water quality requirements
If limescale deposits have formed because of a failure
to observe the requirements of Directive VDI 2035 the
service life of the installed heating appliances will, in
most cases, already have been reduced.
Removing the limescale deposits is one option for
restoring operational viability. This measure must be
carried out by a qualified contractor. Inspect the heat-
ing system for possible damage prior to returning it into
use.

Prevention of damage due to corrosion on the water side

The corrosion resistance of ferrous materials on the
heating water side of heating systems and heat gener-
ators depends on the absence of oxygen in the heating
water. The oxygen introduced into the heating system
with the first fill and subsequent top-ups reacts with the
system materials without causing damage.
The characteristic blackening of the water after a cer-
tain time in operation indicates that there is no more
free oxygen present. The technical rules and in partic-
ular Directive VDI 2035-2 therefore recommend that
heating systems are designed and operated so that a
constant ingress of oxygen into the heating water is
prevented.
During operation, oxygen can normally only enter due
to:
Open expansion vessels receiving a flow
■
Negative pressure in the system
■
Gas-permeable components
■
Sealed unvented systems
vessel offer good protection against the ingress of
–
airborne oxygen into the system, if correctly sized and
operating at the correct pressure.
In all operating states and at all points in the heating
system, including the intake side of the pump, the
pressure must be higher than atmospheric pressure.
Check the pre-charge pressure of the expansion ves-
sel at least during the annual service. For pressure
maintaining systems, see page 10.

Using antifreeze in boilers

Viessmann boilers are designed and built for water as
a heat transfer medium. To protect boiler systems from
frost, it may be necessary to treat the boiler water or
circulating water with antifreeze.
When doing so, observe the following:
In general, follow the specifications given by the anti-
■
freeze manufacturer.
The properties of antifreeze and water are very dif-
■
ferent.
The temperature stability of the antifreeze must be
■
sufficient for the particular application.
(cont.)
e.g. with an expansion
–
It is essential that the faulty operating parameters are
corrected to prevent renewed formation of excessive
scale deposits.
The use of gas-permeable components, e.g. permea-
ble plastic pipes in underfloor heating systems, should
be avoided. Provide system separation if such compo-
nents are nevertheless used. This must separate the
water flowing through the plastic pipes from other heat-
ing circuits, e.g. from the boiler, by the provision of a
corrosion-resistant heat exchanger.
No further anti-corrosion measures are required for
sealed hot water heating systems, subject to the above
points being observed. However, take additional pre-
cautions where there is a risk of oxygen ingress, for
example by adding oxygen binder sodium sulphite (5 -
10 mg/l into the excess). The pH value of the heating
water should be between 9 and 10.5.
Different conditions apply to systems that contain alu-
minium components.
Where chemicals are used as part of the corrosion
protection, we recommend that the manufacturer of the
chemicals issues a certificate of suitability of the addi-
tives with regard to the boiler materials and the materi-
als of the other heating system components. We rec-
ommend you refer questions regarding water treat-
ment to a qualified contractor.
For further details, see Directives VDI 2035-2 and
EN 14868.
Check the compatibility with sealing materials. If
■
other sealing materials are used, take this into
account when designing the system.
Antifreeze developed especially for heating systems
■
contains inhibitors and buffer substances for corro-
sion protection as well as glycol. When using anti-
freeze, always observe the manufacturer's instruc-
tions regarding minimum and maximum concentra-
tions.
Water quality
21