Load Operation; Heat-Up Preparations - Viessmann VITOLIGNO 250-S Operating Instructions Manual

Start-up/shutdown
Boiler operating phases
The operating phases are shown on the programming
unit display. After heat up, the boiler runs through the
following operating phases in sequence:
Heat up
■
■

Load operation

Heat up
After charging and igniting the fuel, the boiler starts up.
Initially, the boiler air dampers are adjusted.
Load operation
From a flue gas temperature above 120 °C or a resid-
ual oxygen content below 15 % (for 2 minutes), the
boiler enters control mode. For this, the residual oxy-
gen content is monitored and the air dampers are con-
tinuously regulated to achieve the set value.
Residual heat utilisation
After combustion of the fuel, the boiler is still warm.
During this phase, the residual heat of the boiler water
is used to supply the heating circuits and DHW heat-
ing. When the temperature of the boiler water is no
longer sufficient for this, the required heat is drawn
from the heating water buffer cylinder. This is achieved
by using the buffer cylinder control valve and provides
up to 9 % increased heat energy yield for the boiler.
Heating water buffer cylinder draw-off
The temperature of the boiler water is too low to supply
the heating circuits and DHW heating with heat. They
are now supplied exclusively from the heating water
buffer cylinder.

Heat-up preparations

Fig. 7
14
■ Residual heat utilisation
■ Buffer drawing
The fuel in the boiler is fully combusted while transfer-
ring the rated heating output to the heating circuits and
the heating water buffer cylinder.
1. Check the heating system pressure at pressure
gauge :
A
If the indicator is resting below the red field, the
system pressure is too low. Top up with water or
notify your local heating contractor.
Minimum system pressure: 1.0 bar (0.1 MPa)
2. Check that the vents in the installation room are
unrestricted.
Note
With open flue operation, the combustion air is
drawn from the installation room.
3. Check that the heating system or the heating water
buffer cylinder can draw off heat. Where necessary,
open the thermostatic valves.