AERCO BMK 2.0 LN October 2012 - Manual (Page 44)

Chapter 3
Benchmark 2.0LN Low NOx Boiler
GF-123
Operation Installation, Operation and Maintenance Manual OMM-0046_0F
Page 44 of 172 AERCO International Inc.● 100 Oritani Dr. ● Blauvelt, NY 10913. ● Ph: 800-526-0288 PR1 10/17/12
3.9 START SEQUENCE
When the Control Box ON/OFF switch is set to the ON position, it checks all pre-purge safety
switches to ensure they are closed. These switches include:
• Safety Shut-Off Valve Proof of Closure (POC) switch
• Low Water Level switch
• High Water Temperature switch
• High Gas Pressure switch
• Low Gas Pressure switch
• Blower Proof switch
• Blocked Inlet switch
If all of the above switches are closed, the READY light above the ON/OFF switch will light and
the unit will be in the Standby mode.
When there is a demand for heat, the following events will occur:
NOTE
If any of the Pre-Purge safety device switches are open, the appropriate
fault message will be displayed. Also, the appropriate fault messages will
be displayed throughout the start sequence, if the required conditions are
not observed.
1. The DEMAND LED status indicator will light.
2. The unit checks to ensure that the Proof of Closure (POC) switch in the downstream Safety
Shut-Off Valve (SSOV) is closed. See Figure 3-3 for SSOV location.
3. With all required safety device switches closed, a purge cycle will be initiated and the
following events will occur:
(a) The Blower relay energizes and turns on blower.
(b) The Air/Fuel Valve rotates to the full-open purge position and closes purge position
switch. The dial on the Air/Fuel Valve (Figure 3-4) will read 100 to indicate that it is full-
open (100%).
(c) The VALVE POSITION bargraph will show 100%.
4. Next, the blower proof switch on the Air/Fuel Valve (Figure 3-5) closes. The display will
show Purging and indicate the elapsed time of the purge cycle in seconds.
5. Upon completion of the purge cycle, the Control Box initiates an ignition cycle and the
following events occur:
(a) The Air/Fuel Valve rotates to the low-fire ignition position and closes the ignition switch.
The dial on the Air/Fuel Valve (Figure 3-6) will read between 25 and 35 to indicate that
the valve is in the low-fire position.
(b) The igniter relay is activated and provides ignition spark.
(c) The gas Safety Shut-Off Valve (SSOV) is energized (opened) allowing gas to flow into
the Air/Fuel Valve.