36
COMMISSIONING
− DHW mode 2 - Tank with thermostat: hot water is stored in
a tank where the temperature is detected by a thermostat
(ON/OFF signal). Either a pump or a 3-way valve can be used
to switch to DHW mode. When the DHW demand is on, the
boiler is PID modulated to achieve the DHW store setpoint.
DHW store setpoint is manually set on the CH/DHW Setpoints
screen (through the Settings screen).
Fig. 36
CH/DHW Setpoints
Temperature summary picture of the DHW tank is available on the
DHW screen, accessible through the Tap (faucet) button on the
Module screen.
Fig. 37
Module Screen
Fig. 38
DHW Screen
4.5.1 Minimum Water Flow (Heat Exchanger Protection)
This unit is self-protected against low water ow. A ow meter
continuously monitors the water ow to each module. If the water
ow decreases below the minimum stated, the burner automat-
ically shuts off.
9
NOTE: Make sure that the pump in the system is free, bled and
rotate in the right direction.
Fig. 39
Rotation pump check
4.5.2 Heating System Pressure Test
If the pressure inside the heating circuit falls below the minimum
pressure for the system (7.5 PSI), the appliance switches off and
the 905PB inner display shows “Low water pressure” to indicate
that it is necessary to restore the correct pressure.
Open the lling valve and check the pressure on the temperature/
pressure gauge of Fig. 40.
The error will disappear when the pressure is back at the right
value. To prevent accidental relief valve openings, ll the heating
circuit slowly.
Temperature/Pressure
Gauge
Fig. 40
Temperature/Pressure Gauge location
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