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Operating information
(continued)
Control inputs and outputs
Room thermostat
The room thermostat input tells the boiler to provide heat for
space heating.
DHW Priority
If a DHW call for heat is received while a Space Heating call
is in progress, the control will start operating in DHW Mode
to move the diverter valve to the DHW position. The control
will not resume Space Heating operation until the DHW call
has ended.
Anti-cycling
After the burner turns off, the control will delay the next
burner cycle for a set time period. The time delay will be
bypassed if the inlet water temperature drops too far during
the delay. The anti-cycling delay does not apply to DHW
calls for heat.
Modulation
The Noble Combi Boiler is capable of modulating its firing
rate from a minimum of 10% to a maximum of 100%. The
firing rate is dictated by the call for heat (i.e., space heating
or domestic hot water), the heating load, and various other
temperature limitations.
Boiler outlet temperature sensor
The Noble Combi Boiler is factory equipped with a boiler
outlet temperature sensor which is also used as the limit
sensor for the heater. During a space heat call for heat, the
outlet temperature sensor is used to control modulation of
the boiler unless a system supply sensor is field installed.
System supply temperature sensor (optional)
An optional factory supplied and field installed system
supply temperature sensor may be used with the Noble
Combi Boiler. When installed, this sensor is used to control
modulation of the boiler during a space heat call for heating.
Boiler inlet temperature sensor
The Noble Combi Boiler is factory equipped with a boiler
inlet temperature sensor.
Combi DHW outlet temperature sensor
The Noble Combi Boiler is factory equipped with a combi
DHW outlet temperature sensor. This sensor is used to
control modulation of the boiler during a DHW call for heat.
When this sensor is missing, limited operation in DHW
Mode is possible by controlling the boiler outlet temperature
to the DHW set point.
DHW flow switch
The Noble Combi Boiler is factory equipped with a DHW flow
switch connected to the control that detects the presence of
DHW water flow rates greater than 0.32 gpm. This input tells
the boiler to provide heat for DHW heating.
Combi diverter valve
The Noble Combi Boiler is factory equipped with a diverter
valve used to route boiler water to the heating system when
in the Space Heating Mode or through the brazed plate heat
exchanger when in DHW Mode. This diverter valve is normally
in the DHW position, thus isolating the boiler from flow in the
heating system.
Boiler pump control
The Noble Combi Boiler is factory shipped with an internal
boiler pump used to generate flow for both space heating and
DHW operation. The boiler pump will run whenever the
burner is firing. The boiler pump will also run during Freeze
Protection and Combi Pre-Heat Modes. The boiler pump will
continue to run for a short time after the burner turns off, the
Freeze Protection Mode ends, or the Combi Pre-Heat Mode
ends.
System pump control
The Noble Combi Boiler is capable of controlling a field
supplied and installed space heating system pump. The system
pump will run whenever there is a space heating call for heat, or
the boiler goes into Freeze Protection Mode. The system pump
will continue to run for a short time after the end of the heat
demand or the Freeze Protection Mode.
Gradient limiting
If during operation of the boiler the outlet water temperature is
rising too quickly, the control will reduce the firing rate to its
lowest setting.
SH rate limiting
The Noble Combi Boiler includes an SH Rate Limiting feature
that limits the maximum modulation during a space heating
call.
Installation & Service Manual
F I R E T U B E C O M B I
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