Product Overview

50
103859-12 - 8/19
MPO-IQ
Installation & Service Manual
When an Outdoor Air Reset Option Card is
installed and there is a DHW call for heat there
is an adjustable DHW Temperature Setpoint
and Priority Timer included. Refer to Table
11B.
b. When ZC_ is set equal to Zone Request (ZR)
When there is no IWH the “ZC” output may be
configured to control a second heating zone.
This is particularly helpful when the home uses
only two heating zones. The boiler control
replaces the need for a two circulator zone
panel. When DHW Terminal Function (dh_) is
set to “ZR” the boiler control’s two circulator
outputs are used to control two independent
heating zones. Refer to Table 12. A "TT"
input causes a call for heat and energizes the
System Circulator output to service heating
zone 1. A second zone’s thermostat may be
wired to the "ZR" input to energize heating
zone 2 circulator wired to the "ZC" output.
Both outputs function independently, "TT" input
controls only the System Circulator output and
the "ZR" input controls only the "ZC" output.
Both inputs cause a boiler call for heat.
c. External Low Limit, Parameter ZC = ELL
The boiler control is capable of functioning
as a warm start control when external limit
control is installed that closes a contact when
boiler water temperature falls below a setpoint.
When an external limit contact closes (boiler
water is cold) the boiler is started and the ZC
and C1 output terminals are de-energized.
When the ZR terminal is de-energized (boiler
water temperature is above setpoint) the
call for heat is ended and the C1 terminal is
released to operation and the ZC terminal is
energized. An External Low Limit Request
is detected by sensing a voltage on the ZR
terminal. Refer to Table 13.
Table 13: External Low Limit, Parameter zc_= ell
Call for Heat Circulator Status
T- T
Input
ZR
Input
C1
Output
ZC
Output
off off off on
on off on on
on on off off
off on off off
9 Operating (continued)