Service manual

70
Installation & Service Manual
13 Troubleshooting
Table 13-1 Troubleshooting Chart - No Display
FAULT CAUSE CORRECTIVE ACTION
No Display
- No 120 vac supplied to unit. • Check external line switch, fuse, or breaker.
• Check wiring harness connection between display
board and main control board. Connect
harness at both points.
- 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 69 of this manual.
No Burner
Operation
- Main control board temperature set point
satisfied.
• Review temperature setting.
- Remote thermostat satisfied. • Review remote thermostat setting.
- Outside air temperature above Warm
Weather Shutdown (WWSD) set point for
main control board.
• Check location of outside air sensor. Check
resistance of outdoor air sensor and compare to Table
13-2B on page 71 of this manual.
- Unit locked out on fault. • Consult display for specific fault. Refer to fault
descriptions on page 73 of this manual for corrective
actions.
Unit Does
Not Modulate
Above 50%
- 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 13-2D on page 71 of this manual.