Product Overview

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103859-12 - 8/19
MPO-IQ
Installation & Service Manual
Figure 33: Boiler Control & Option Panel Orientation
A. BOILER SEQUENCE OF OPERATION
1. The boiler's sequence of operation is shown in Table
9.
2. When there is a call for heat the boiler control
starts the system circulator and the thermal purge
(circulator pre-purge time) begins. If the time is
completed or boiler temperature is less than the
Start Temperature (140 F default) the start sequence
continues by energizing the oil primary to operate the
following sequence: blower is started and operates
for pre-purge time; spark is energized and fuel valve
is opened for ignition trail time; burner fires until the
thermostat is satisfied.
3. If the thermostat is not satisfied and the Operating
Setpoint (SP) is reached the system circulator will
continue to operate and the burner will stop. When
the boiler water temperature drops below the setpoint
less the differential setting the burner will restart.
4. After the thermostat is satisfied the burner and
circulator are stopped.
5. When an indirect water heater aquastat call for
heat is wired to the DHW input the control starts
the Domestic Hot Water circulator and when boiler
temperature is less than the operating setpoint
energizes the oil primary to turn on the burner
without circulator pre-purge delay.
6. On water boilers equipped with a High Limit Option
Card, if boiler water temperature exceeds the high
limit setting, the system pump will continue to
operate, and the burner will stop. When the boiler
water temperature drops below the High Limit Card
differential setting, (15°F), the burner will restart.
7. On water boilers equipped with a LWCO Option
Card, if level probe senses a low water condition,
the system pump will continue to operate and the
Status Code Displayed in STA Mode
STA
Status Description
1
Standby
(burner off,
circulator off)
No call for Heat Detected.
1
Standby
(burner off,
circulator on)
Either condition is true:
a. Call for heat detected and boiler
temperature higher than operating
setpoint.
b. Call for heat is detected and boiler
temperature higher than start tempera
ture (140°F default) and circulator pre-
purge time has not expired.
4**
Pre-purge The blower is turned on for a valve-on delay.
6*
Trial For Ignition
(TFI)
The igniter is turned on and the fuel valve is
opened. A flame must be established within
the trial for ignition time.
7*
Carryover
Once flame is established, the ignition remains
on for 10 seconds to ensure flame stability and
then turns off.
8
Running
The burner runs until the call for heat is satisfied.
The burner is then sent to burner motor-off
delay, as applicable, or it is shut down and
sent to standby.
9*
Post-purge
The fuel valve is closed and the burner motor is
kept on for an off delay time before the control
returns the burner to standby.
10*
Retry / Recycle
Delay
If the flame is lost while the burner is firing,
the control shuts down the burner, enters a
recycle delay, and then repeats the ignition
steps outlined above. If the flame is lost three
times in a row, the control locks out to prevent
cycling with repetitious flame loss caused by
poor combustion.
14*
Hard Lockout
If flame is not sensed by the end of the TFI, the
control shuts down on safety lockout and must
be manually reset. Press and hold reset button
for 30 seconds to reset the restricted lockout.
15*
Waiting for Limit to
Close
Heat request present and start sequence is
halted due to an open limit. Open limits include
high water temperature or low water detected
by IQ Option Cards.
16*
Flame Present Out
of Sequence
Flame signal is still present when expected to
be 0 (no flame).
17
Self Test Control internal checking.
Table 9: Sequence Of Operation
9 Operating