Patterson-Kelley MOD-04 ユーザーズマニュアル

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14.  When the load is below the low fire rating of the 

boiler the boiler will continue firing and the out-
let water temperature will rise until it reaches 
the set point + hysterises value.  At this point 
the operating control switch opens and the com-
bustion control is de-energized at Terminal 6 
and the indicator for HEAT is turned off.  This 
action also de-energizes Terminal 9 thus closing 
the main gas valve and the air gas ratio control 
valve.  Relay-1 and 2 are de-energized which 
applies power to the close terminal of the air 
damper motor.  The air damper closes. 

15.  When the water temperature is reduced by the 

load on the system, the operating control switch 
will close again.  The operating sequence will 
recycle to step 5, provided the limits on water 
flow, gas pressure and high temperature are all 
met. 

 

5.5.2  IRI Modulating 
 
1.  When the On/Off (Main power) switch is turned 

on, the switch illuminates.  Power is provided to 
the flame safeguard control, the temperature 
control, and through the flame safeguard control 
to the damper close terminal.  Power is also ap-
plied through the proof of closure switch on the 
air gas ratio control, and to the  “start logic 
string”  a series of normally closed switches, in-
cluding water flow, gas pressure, high stack 
temp, high limit temperature, and operating 
temperature to the flame safeguard programmer. 

2.  The water flow limit switch is closed when 

there is water flow through the boiler. 

3.  Note: The closing of this switch does not prove 

that flow is adequate.  Refer to Technical Data 
Sheet # TD110 for proper flow requirements.   

4.  When gas pressure is available, the low gas 

pressure limit switch is closed.  Manual reset is 
required following conditions resulting in low 
gas pressure. 

5.  When the temperature sensed by the high limit 

temperature control is below the set limit, the 
switch is closed.  Manual reset is required fol-

lowing conditions exceeding high limit tempera-
ture. 

6.  When heat is required as indicated by the outlet 

water temperature, power is applied to Terminal 
6 of the programmer, which initiates the burner 
ignition and operation sequence. 

7.  The flame safeguard control first energizes 

Terminal 5 which energizes control relay R1, 
energizes  the motor contactor for the blower 
motor, and supplies power to the air flow 
switch, which initially shows low air flow with 
the “Low Air “ indicator.  This indicator will 
remain on until air flow is sensed. Terminal 12 
is also energized which drives the air damper to 
the open position. When the damper motor is at 
the full open position, the high fire limit switch 
is made which energizes the high fire switch in-
put terminal 19 on the flame safeguard control.  

8.  Once sufficient airflow is indicated by the air 

flow switch, Terminal 7 of the flame safeguard 
control is energized.  If the high fire switch and 
proof of closure switch are in the correct state, 
this starts the Prepurge period.  The combustion 
chamber is Prepurged for 30 seconds. 

9.  When the Prepurge time period elapses the 

flame safeguard control energizes terminal 14, 
which drives the damper motor through the po-
sition switch to the start position. 

10.  When the damper motor is at the start position, 

the start position limit switch is made, which 
energizes the low fire switch input terminal 18 
on the flame safeguard control. A 10-second 
“trial for ignition” period is initiated with both 
Terminal 8 and 10 being energized. Terminal 10 
of the combustion control powers the ignition 
transformer.  The transformer output creates a 
spark at the igniter.  Terminal 8 powers the pilot 
gas valve. 

11.  When a pilot flame is detected by the UV scan-

ner a signal is sent to the combustion control.  
When this signal is detected, Terminal 10 of the 
combustion control is de-energized terminating 
the spark. 

12.  After the 10 second  “Pilot Flame Establishing” 

period, if pilot flame has been established, Ter-