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XIV. Troubleshooting
A. Troubleshooting problems where no error code is displayed:
TABLE 14.1: NO ERROR CODE DISPLAYED
CONDITION POSSIBLE CAUSES
Display Blank, Fan off, LWCO lights off
• No 120VAC Power at boiler. Check breaker and wiring between breaker panel
and boiler
Display Panel Blank, Fan running
• Loose 120VAC connection wiring between boiler J-Box and MCBA
• Blown “F1” fuse in MCBA (see Figure 13.2 for location). Replace with 5A fuse
provided
Display reads “U.125” continuously, Fan running
• Defective AT250 transformer
• Blown “F3” fuse in MCBA (see Figure 13.2 for location). Replace with 4A slow-
blow fuse provided
Boiler not responding to call for heat, Status code on
display =”0” (see Figure 11.1)
• Boiler is not seeing call for heat. Check thermostat or zone wiring for loose
connection, miswiring, or defective thermostat/zone control.
Boiler fi res, but display panel is blank
• Loose ribbon cable
• Defective display
WARNING
Turn off power to boiler before replacing fuses or working on wiring.
Figure 14.2: MBCA Fuse Location