3
Troubleshooting
(continued)
Service Manual
34
Table 3-1
Troubleshooting Chart - No Display
FAULT
CAUSE
CORRECTIVE ACTION
No Display
- No 120 vac supplied to unit.
• Check external line switch, fuse, or breaker.
• Check 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 33 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
3-2B on page 35 of this manual.
- Unit locked out on fault.
• Consult display for specific fault. Refer to fault
descriptions on page 37 of this manual for corrective
actions.
Unit Does Not
Modulate
Above 50%
- Ramp delay active.
• Check ramp delay parameter settings. Optional PC
software required.
• Turn ramp delay feature off. See page 23 of this
manual for instructions on how to turn this feature off.
- Boiler 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 3-2D on page 35 of this manual.
Summary of Contents for Knight 151 - 211
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