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Service Manual
3 Troubleshooting
Table 3A Troubleshooting Chart - No Display
FAULT CAUSE CORRECTIVE ACTION
No Display
- No 120 VAC supplied to unit. • Check external line switch, fuse, or breaker.
• Check position of ON/OFF switch. Turn switch to the
ON position.
• Check 120 VAC through the ON/OFF switch.
• Check wiring harness connection between display
board and main control board. Connect
harness at both points.
- No voltage through the switch. • Replace switch.
- Bad display board. • Replace board.
- Bad main control board. • Replace the main control board.
- Blown fuse. • Replace fuse F3 on the main control board, see
page 21 of this manual.
No Burner
Operation
- Main control board temperature set point
satisfied.
• Review temperature setting.
- Remote thermostat satisfied. • Review remote thermostat setting.
- Unit locked out on fault. • Consult display for specific fault. Refer to fault
descriptions on page 25 of this manual for corrective
actions.
Unit Does Not
Modulate Above
50%
- Water heater controlled by BMS.
• Check BMS parameter settings. Optional PC software
required.
- Flue sensor open.
• Verify that the flue sensor is located in the flue outlet.
• Check wiring connections at the flue sensor.
• Check the resistance of the flue sensor and compare
to Table 3C on page 23 of this manual.