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XIV: Troubleshooting
Figure 58: MBCA Fuse Location
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 58 for location). Replace with 5A fuse provided
Display reads “U.125” continuously, Fan running
• Defective AT250 transformer
• Blown “F3” fuse in MCBA (see Figure 58 for location). Replace with 4A slow-blow fuse
provided
Boiler not responding to call for heat,
Status code on display =”0” (see Figure 50)
• Boiler is not seeing call for heat. Check thermostat or zone wiring for loose connection,
miswiring, or defective thermostat/zone control.
Boiler res, but display panel is blank
• Loose ribbon cable
• Defective display
Table 28: No Error Code Displayed
A. Troubleshooting problems where no error code is displayed. Refer to Table 28 for problems and possible causes.
WARNING
Turn off power to boiler before replacing fuses or working on wiring.