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because low oxygen input into the heating circuit can
also be tolerated.
In general, when the system is filled with deionised
water, the pH value sets itself within the ideal range due
to “self-alkalinisation”. If necessary, a pH value of 8.2
can be very easily alkalised by adding chemicals. In this
way, optimum protection of the entire heating system is
achieved.
MONITORING
Analytical recording and monitoring of the relevant
water values and the added active conditioning
substances is of decisive importance. Therefore, they
should be monitored regularly using appropriate water
test equipment
Flush, fill and bleed the heating circuit…
In addition, bleed the condenser of the heat pump…
•
Open the lower facing panel…
•
Open the bleed valve…
Following bleeding, close the lower facing panel.
If the water is softened before the heating is filled, in
accordance with the VDI 2035 guidelines, no scale
can form. This effectively and permanently prevents
limescale deposits and the resulting negative effects on
the entire heating system.
CORROSION – AN UNDERESTIMATED PROBLEM
VDI 2035, Part II, deals with the problem of corrosion.
Softening the heating water can prove to be insufficient.
The pH value can significantly exceed the limit of 10.
pH values higher than 11 can set in, which even damage
rubber seals. The VDI 2035, Part 1 guidelines are
fulfilled, however, VDI 2035, Part 2 suggests a pH value
between 8.2 and maximum 10.
If aluminium materials are used, which is the case in
many modern heating systems, a pH value of 8.5 must
not be exceeded, because otherwise there is a threat
of corrosion – and aluminium is attacked without the
presence of oxygen. Therefore, apart from softening
the heating fill and additional water, the heating water
should also be appropriately conditioned. This is the
only way to comply with the VDI 2035 requirements and
the recommendations and installation instructions of the
heat pump manufacturer.
Part 2 of VDI 2035 also points out the reduction in total
salt content (conductivity). The risk of corrosion is far
lower if deionised water is used than is the case if the
system is operated with salty, i.e. softened water.
Even if the water has been softened beforehand, it
contains dissolved, corrosion-promoting salts, which act
as electrolytes due to the use of different materials in
the heating system and therefore accelerate corrosion
processes. This can ultimately result in pitting.
Contamination and deposits in the heating circuit can
cause malfunctions
RINSE, FILL AND BLEED THE HEATING CIRCUIT AND
HOT WATER BUFFER TANK
To bleed the hot water tank, the heating circuit and hot
water circuit must be rinsed simultaneously.
ON THE SAFE SIDE WITH LOW-SALT OPERATION
The problems listed above do not occur at all with
low-salt operation, as neither corrosive salts such as
sulphates, chlorides and nitrates nor alkalising sodium
hydrogen carbonate are in the heating water. The
corrosive properties of deionised water are very low
and in addition, fur cannot form in the boiler. This is the
ideal approach for closed heating circuits, in particular,
