16
Mode 2 (Type H Units Only)
This mode selection is for hydronic heating systems
with single or multiple boilers (Maximum 4 boilers) in
primary/secondary piping configuration with or without
Outdoor Air Reset (S4) with indirect DHW on the sys-
tem loop (with or without priority). The system
temperature is controlled by the System sensor (S3).
The Indirect DHW sensor (S5) determines the indirect
call/tank setpoint. The system temperature is boosted
to Target Max when using the Indirect DHW sensor
(S5) during an indirect call for heat. Priority mode tog-
gles off the System Pump (P2) when an indirect call for
heat is present. The Boiler Pump (P1) runs during any
call for heat. The Indirect DHW Pump (P3) runs during
an indirect call for heat with no “off” delay. The Boiler
Pump (P1) and System Pump (P2) delay “off” as user
defined in the
ADJUST
menu. The System Pump (P2)
runs whenever the system is enabled for heating and
the outdoor air temperature is lower than the WWSD
temperature setting (if utilized) unless an indirect call
for heat is present with priority.
Fig. 12: MODE 1 - Single Boiler with
Primary/Secondary Piping
Fig. 14: MODE 2 - Single Boiler with Indirect
on System Loop
Mode 1 (Type H Units Only)
This mode selection is for hydronic heating systems
with single or multiple boilers (Maximum 4 boilers) in
primary/secondary piping configuration with or without
Outdoor Air Reset (S4). The system temperature is
controlled by the System sensor (S3). The Boiler
Pump (P1) runs during any call for heat. The System
Pump (P2) runs whenever the system is enabled for
heating and the outdoor air temperature is lower than
the warm weather shut down (WWSD) temperature
setting (if utilized). The Boiler Pump and System Pump
are delayed “off” as user defined in the
ADJUST
menu.
NOTE:
MODE 1 can also be used for process heat-
ing applications in conjunction with a buffer/storage
tank when operating temperatures above 160
°
F are
required. Care must be given to ensure water hard-
ness is no more than 15 grains per gallon for scale
free operation.
Fig. 13: MODE 1 - Boiler Cascade with
Primary/Secondary Piping
Summary of Contents for 503A
Page 43: ...43 WIRING DIAGRAM Models 503A 2003A...
Page 59: ...59...
