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P/N 42-9472 Copyright 2008 Mestek, Inc.
Cast iron condensing boiler
Cast iron condensing boiler
— Control manual
Method 3: External 4-20ma control
(continued)
3
4-20mA operation
A 4.02 mA current signal will start the boiler, at low fi re. A
20mA signal will cause the boiler to go to full input.
Between these input signal limits, the boiler modulates. Th
e
boiler fi ring rate percentage is equal to the percentage of the
signal between 0 and 20 mA. Example, a signal of 12 mA is
60% of 20 mA, so the boiler fi ring rate would be 60% of max.
In addition to the 4-20mA signal, the remote controller
must also close a contact across each boiler’s Remote En-
able contact in order for the boiler to fi re.
See Figure 16, page 19 for wiring. Notice that the boiler 4-
20mA terminals are wired in series.
IAR (Indoor Air Reset) wiring —
apply ONLY if using space heating
override mode
IAR can only be used if one or more of the boilers is wired
and piped for override operation. Override would occur
when a contact closed across the Heat Demand terminals.
While this contact is closed, the boiler will operate based on
local control, including feedback for IAR if wired.
If override operation will be used, and you want to operate
with IAR when in override mode, follow the instructions
under Method 1 in this manual to wire for IAR.
Sensor wiring
Header sensor cannot be used when the boilers
are confi gured for remote operation by a 24-mA
source.
Outdoor reset application can be done only in over-
ride mode
— To operate with outdoor reset, purchase and
install an outdoor sensor. Mount the sensor such that it is
shielded from direct sunlight if possible and not likely to be
covered by snow drift s or debris. Connect the outdoor sen-
sor 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 over-
ride mode by closing the Heat Demand terminals.)
Return water temperature sensor
— Th e return wa-
ter 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 — ONLY if using DHW
override mode
The boiler (or boilers) must be piped with isolation
valves and wired for override operation
. Override of
the 4-20mA input will occur if a contact closes across the
boiler’s DHW Demand terminals.
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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 applica-
tions not covered.
Th e circulator used for DHW must be operated by a circula-
tor relay or zone controller 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 con-
nection 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.)External interlocks
Wire external limits and fl ow switch, when used, as shown
in Figure 17, page 20.
Th e combustion air interlocks cannot be used when operat-
ing with a 24-mA remote control. Combustion air damper
control must be done by the remote control system.
Overrides — Control priorities
Th e 200i control can provide override operation for any or
all member boilers. Th is requires the boilers be piped with
appropriate isolation piping and controls.
Override is done by closing a contact across the Heat De-
mand or DHW Demand terminals of any boiler. Th ese
priority inputs override all 4-20mA input controls to the
boiler.
DHW Demand
— Th e DHW Demand closure takes prior-
ity for ALL boilers, including the master and all members.
When DHW Demand closes, the boiler or boilers immedi-
ately switch to DHW operation, including sett ing the water
temperature to the DHW Setpoint.
Space heating, Heat Demand
— If any member boiler
sees closure across its Heat Demand terminals it will begin
operation in space heating mode independently of com-
mands from the 4-20mA input source.
Do not wire boilers for override operation unless
the piping design provides automatic isolation of
the overriding boilers.
Override operation control setup — Boilers
must be set up with operating parameters
necessary during their override operation; i.e.,
local setpoint, DHW setpoint, etc.
Summary — priority sequence is:
Priority 1 = DHW Demand
Priority 2 = Heat Demand
Priority 3 = 4-20mA Input/Enable
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