Viessmann VITOCROSSAL 300 Service Instructions Manual page 15

Further details regarding the individual steps
The expansion vessel must have the fol-
lowing minimum size, subject to the
boiler output:
■ up to 300 kW: 50 l
■ up to 500 kW: 80 l
■ up to 1000 kW: 140 l
The expansion vessel reduces the fre-
quency and severity of pressure fluctua-
tions. This improves the runtime of the
pressure maintaining pump and there-
fore increases the operational reliability
and service life of the system compo-
nents.
Failure to observe these recommen-
dations may result in damage to the
boiler or to other system compo-
nents.
Carry out all checks in accordance with
the manufacturer's instructions. Limit
pressure fluctuations to the lowest pos-
sible differential. Cyclical pressure fluc-
tuations and more significant pressure
differentials point towards a system fault.
Immediately remedy such faults, other-
wise other heating system components
may be damaged.
Commissioning, inspection, maintenance
Expansion vessels
1. Drain the system or close the cap
valve on the expansion vessel and
reduce the pressure until the pres-
sure gauge indicates "0".
Note
The pre-charge pressure of the
expansion vessel (p
the static system pressure (p
(= static head) and a supplement
(p = p + supplement).
0 St
The supplement depends on the high
limit safety cut-out setting.
Supplements are as follows. For high
limit safety cut-out setting
100 °C: 0.2 bar (20 kPa)
110 ºC: 0.7 bar (70 kPa)
2. If the pre-charge pressure of the
expansion vessel is lower than the
value calculated according to the
given formula, top up with nitrogen
until this value has been achieved.
3. Refill with water until the charge pres-
sure is 0.2 (20 kPa) higher than the
pre-charge pressure of the expan-
sion vessel when the system is cold.
4. Mark this value on the pressure
gauge as the minimum charge pres-
sure.
(cont.)
) is made up of
0
)
St
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