25
5584 109 - 10
Vitocrossal 200 CM2 186 to 311 Service
Check proper expansion tank and system pressures
Total output (MBH) Total Hardness (ppm as CaCO
3
)
> 1 to
680
200
> 680 to
2050
150
1. Drain system or close cap valve on the diaphragm
expansion tank and reduce the pressure until the pressure
gage indicates “0”.
2. 60°F (15.5°C) water fill pressure must equal diaphragm
expansion tank pressure.
CAUTION
Damage on boiler or other system components may
result if these recommendations are not followed.
IMPORTANT
The diaphragm expansion tank must be able to hold the
heating water expansion volume inside the boiler, and must
be properly sized for the system.
CAUTION
Carry out all check in accordance with the expansion
tank manufacturer’s instructions. Limit pressure
fluctuations to the lowest possible differential. Cyclical
pressure fluctuations and greater pressure differentials
indicate a system fault. Immediately remedy such
faults, otherwise other heating system components
may become faulty.
IMPORTANT
Carry out this test on a cold system.
See expansion tank manufacturer’s instructions.
This diaphragm expansion vessel reduces the frequency
and severity of pressure fluctuations; the service life
of the circulating pump is improved and therefore
the operational reliability and service life of system
components increased.
Water Quality
The lifetime of the entire heating system is influenced by
the water quality. A water treatment system will protect
against damages caused by corrosion and lime formation.
Hard water conditions (i.e. calcium carbonate) must be
avoided as it will cause deposits to accumulate on the
heat exchanger surfaces.
If in any doubt about the water quality, please have a
proper water analysis done. Check with regional chemical
suppliers for boiler water treatment or with Viessmann
Manufacturing Company Inc. directly.
The pH value of the heating water should be between 8.2
and 9.5
Fan pressure monitoring function (air pressure switch 1)
The switching threshold of air pressure switch 1 is
monitored in all fan ramp-up phases and checked in
modulating burner operation. This minimizes pre-purge.
Air pressure switch
A
triggers a fault shutdown of the
burner control unit under the following circumstances:
■
If the idle state check is not successful after
approximately 5 minutes.
■
If, during the pre-purge phase, the air pressure
is outside the permissible range (tolerance time
approximately 5 minutes).
■
If, during operation, the air pressure switch fails or
the air pressure is outside the permissible range.
The fault shutdown is shown with fault display “F F5“
and “F F7“ on the burner control unit (see page 48) and
can be rectified by pressing reset button
R
B
.
Boiler model
Air Pressure Switch 1 Adjustment Value
in mbar
186
1
246
311
Note:
The air pressure switch is a normally open contact
that closes when pressure rises above its setpoint.
Once the contact closes it will trigger a safety
shutdown of the burner.
Further Details Regarding the Individual Steps
Diaphragm Expansion Vessel and System Pressure
Burner Service
