8
P/N 42-9472 Copyright 2008 Mestek, Inc.
Cast iron condensing boiler
Cast iron condensing boiler
— Control manual
Figure 6
Indoor Air Reset wiring to IAR terminals with
4-wire zone valves and no zone controller
(see Figure 7, page 9 for terminal block
6
location)
Method 1: SmartCycle modulation – local control
(cont.)
1
IAR (Indoor Air Reset) wiring, when used
Heat Demand terminal connections — Th e end switch leads from the zone valves
must connect to the Heat Demand terminals on the electrical connection board as
shown in Figure 7, page 9.
See Figure 6 for typical wiring to the IAR inputs when using 4-wire zone valves
without a zone controller. For other applications, such as circulator relays or zone
controllers, see Appendix A in the Boiler manual.
Polarity
— Th e connections to the
IAR
positive terminals (
IAR +
)
must be to the same location on the zone valve as the thermostat wire,
as shown in Figure A1. Th e connections to the
IAR
negative terminals
(
IAR –
) must be from the zone valve terminal connected to the 24VAC
common line, as shown. Connecting the wires incorrectly can cause the
transformer to be shorted out and damaged. Verify the wiring with a
voltmeter.
Always use a voltmeter to check the leads coming from the end switches
of the zone valves. With the thermostat calling for heat, connect the
voltmeter leads across the wires coming from the end switches. If
the meter shows a voltage reading, the zone valve wires are incorrect.
Change the wiring and retest. DO NOT connect the wires to the boiler
until you have tested as described. Incorrect wiring can damage the
boiler control or other system components.
If there is only one transformer feeding all of the zone valves in the system, you can
omit the wires to the
IAR
negative terminals (
IAR –
) on all but one of the zone
valves. Th is is because these terminals are jumpered internally on the electrical
connection board. If there is more than one transformer, provide one wire from
each transformer common side to one of the
IAR
negative terminals (
IAR –
).
Sensor wiring
Header sensor is required
— A header sensor must be installed in the system
supply piping.
Connect the header sensor ONLY to the master boiler
. Install
the header sensor in an immersion well. Locate the sensor where it will accurately
sense the system water supply temperature. Connect the sensor leads to the electri-
cal connection board as shown in Figure 8, page 10.
Outdoor reset application
— To operate with outdoor reset, purchase and in-
stall an outdoor sensor. Mount the sensor such that it is shielded from direct sun-
light if possible and not likely to be covered by snow drift s or debris. Connect the
outdoor sensor leads to the master boiler’s electrical connection board as shown
in Figure 8, page 10. (Member boilers could have their own outdoor sensor if they
will be operated in override mode by closing the Heat Demand terminals.)
Return water temperature sensor
— Th e return water temperature sensor
is optional, only needed if you want to automatically control the boiler postpurge
pump cycle time. Install the sensor in a well in the boiler return piping. Connect
the sensor leads to the electrical connection board as shown in Figure 8, page 10.
Each boiler requires a return water temperature sensor.
DHW wiring
To operate the boiler for domestic water heating with a storage tank, install and pipe
the tank according to the tank manufacturer’s instructions and the recommended
piping diagrams in this manual. Consult the factory for applications not covered.
Th e circulator used for DHW must be operated by a circulator relay or zone con-
troller that is activated when the tank aquastat calls for heat.
Connect the tank aquastat terminals across the DHW DEMAND terminals on the
master boiler’s electrical connection board as shown in Figure 7, page 9. (Member
boilers could be connected to tank aquastats if they are piped appropriately and
intended to operate in override mode.)
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