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Operating information
Installation & Service Manual
Sequence of operation
Th
e cold domestic water enters the plate heat exchanger through
the DHW inlet connection, fl ow switch, and strainer. Cold
water fl ows through the plate heat exchanger, where it is heated
by hot boiler water, and then discharged through the Domestic
Hot Water (DHW) outlet connection.
Heated boiler water is supplied from the primary combustion
heat exchanger through the diverter valve into the plate heat
exchanger. Th
e boiler water heats the colder domestic water,
and is then returned to the primary heat exchanger through the
pump.
While operating in DHW Mode, the diverter valve prevents
water from fl owing through the boiler outlet connection to
the heating system. Boiler water is circulated inside the unit
between the plate heat exchanger and the primary combustion
heat exchanger.
Th
e diverter valve is normally in the DHW position when the
unit is in Standby, thus isolating boiler water from fl owing to the
heating system. When there is a space heating call, the diverter
valve will move to the space heat position allowing boiler water
to fl ow from the primary combustion heat exchanger through
the boiler outlet connection to the heating system, bypassing
the plate heat exchanger. Th
e internal pump is used to circulate
water in both Space Heating and DHW Modes.
Space heat temperature regulation
Operating temperature (target)
The boiler control module senses water temperature and
regulates boiler firing rate to achieve a target temperature.
The target temperature is calculated as described in this
section under
"Outdoor Reset Operation"
when the outdoor
sensor is connected. The maximum target temperature
can be limited by the installer using the MAX SH SETPT.
This temperature can be set between 32°F and 190°F. If the
outdoor sensor is shorted or not properly installed, the target
temperature is fixed at the SH SETPT (Cold Day).
High limit operations
The Noble Combi Boiler is equipped with an adjustable
automatic reset high limit and a manual reset high limit. The
automatic reset high limit has a maximum set point of 200°F
and the manual reset high limit has a maximum set point of
210°F.
Low water cutoff protection
1. The boiler control module uses temperature sensing of
both supply and return ports of the heat exchanger. If the
flow rate is too low or the outlet temperature too high,
the control module modulates and shuts the boiler down.
This ensures boiler shutdown in the event of low water or
low flow conditions.
2. Some codes and jurisdiction may accept these integral
features of the control in lieu of requiring an additional
limit control or low water cutoff. Consult local
jurisdiction to determine. A low water cutoff is available
from the factory (100173646).
F I R E T U B E C O M B I
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