Patterson-Kelley MACH-05 manual The Loss of Power, 5.4SEQUENCE OF OPERATION, 5.5TROUBLESHOOTING

MACH® Series Gas-Fired Boiler

5.4SEQUENCE OF OPERATION

1.When the On/Off (Main power) switch is turned on, power is provided through a circuit breaker to the boiler control and the combustion blower. The boiler control powers a 24 V transformer. The boiler control supplies 24 V power through a high limit temperature switch and a low water level control.

2.The low water level control is closed when there is water in the boiler up to the probe.

3.When the temperature sensed by the high limit temperature control is below the set limit, the switch is closed. Manual reset of the switch is required following conditions exceeding high limit temperature.

4.If either the high limit temperature control or the low water level control is open, the boiler control locks out and indicates E 12 on the display.

5.Depending on the settings in the boiler control, a heat request is generated.

6.The controller checks that the low air pressure switch is open indicating no airflow. The blower is driven towards the prestart fan speed. When the air pressure switch closes the 15 second prepurge time is started, and the blower is driven toward the ignition speed.

7.After the 15 second prepurge the gas pressure switch circuit is checked to ensure the gas pressure is within design parameters.

Maintenance

10.The unit modulates between the low fire setting and the high fire setting to maintain the desired outlet water temp set point.

11.When the load is below the low fire rating of the boiler the boiler will continue firing and the outlet water temperature will rise until it reaches the set point + temperature differential. At this point the burner is turned off, and the fan continues to run to post purge the boiler for 15 seconds.

12.When the water temperature is reduced by the load on the system, a heat request is again generated. The operating sequence will recycle to step 6, provided the limits on water level, gas pressure and high temperature are all met.

5.5TROUBLESHOOTING

The MACH Series boiler will display service codes to indicate some problems with the boiler. There are two types of lockouts the control may experience: manual reset lockouts requiring an operator to press the reset button, and automatic reset lockouts, where the control will automatically attempt to restart the boiler. A listing of service codes is included at the end of this section.

Should the unit fail to operate, call a qualified service technician to troubleshoot the problem and implement corrective action.

8.If there are no lockouts then when the blower speed is within 200 rpm of the ignition fan speed, a trial for ignition period of 3 seconds is initiated. The internal spark generator and the gas safety shut off / control valves are energized.

9.The internal spark generator is de-energized .3 seconds before the end of the trial for ignition period. After the trial for ignition period, if a flame signal is detected by the flame rectification system, the control initiates a flame stabilization period of 5 seconds at the ignition rpm of the fan. The fan is driven to low fire for 1 minute before the boiler is released to modulation.

The Loss of Power

In the event of a power failure (or when the On/Off switch is in the Off position), the display panel is not illuminated and the entire system is de-energized, closing all automatic valves and halting all boiler operations. When power is restored the sequence of operation will resume at Step 5, provided that all the limits are satisfied. If any manual reset lockout was present when the power is lost, the display will flash E 04 when the power is resumed. This indicates that the control was in lockout mode but does not indicate which service code was present.

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