Patterson-Kelley MOD-04 owner manual Modu-FireGas-Fired Boiler Maintenance, IRI Modulating

Modu-Fire®Gas-Fired Boiler Maintenance

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-

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