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I-UBX-UBZ-UDX-UDZ (03-21) 1034344-0
TROUBLESHOOTING—CONTINUED
General Troubleshooting
Refer to Table 25 for general troubleshooting symptoms, probable causes, and remedies.
Table 25. General Troubleshooting
Symptom Probable Cause Remedy
Venter
motor will
not start
1. No power to unit Turn ON power and check supply fuses or circuit breaker
2. No 24V power to integrated circuit board Turn up thermostat
Check control transformer output
3. Integrated circuit board fuse blown Correct cause and replace fuse (3A, type ATC or ATO, 32VDC)
4. No power to venter motor Tighten connections at circuit board and/or motor terminals
5. Integrated circuit board defective Replace integrated circuit board
6. Defective venter motor Replace venter motor (refer to Venter Motor and Wheel Assembly
Maintenance section)
Burner will
not light
1. Manual valve not open Open manual valve
2. Air in the gas line Bleed gas line (initial startup only)
3. Gas pressure too high or too low Supply pressure should be 5–14 IN WC for natural gas or 11–14 IN WC for
propane
4. No spark Perform following:
a. Loose wire connections Ensure that all wire connections are solid
b. Transformer failure Ensure that 24V power is available
c. Incorrect spark gap Maintain spark gap at 1/8 inch
d. Spark cable shorted to ground Replace worn or grounded spark cable
e. Spark electrode shorted to ground Replace ceramic spark electrode if it is cracked or grounded
f. Burner not grounded Ensure that integrated circuit board is grounded (terminals P1–9)
g. Circuit board not grounded Ensure that integrated circuit board is grounded to furnace chassis
h. Unit not properly grounded Ensure that unit is properly field grounded to earth ground and properly phased
(L1 to hot lead L2 to neutral)
i. Integrated circuit board fuse blown Correct cause and replace fuse (3A, type ATC or ATO, 32VDC)
j. Faulty integrated circuit board If 24V power is available to integrated circuit board and all other causes have
been eliminated, replace board
5. Lockout device interrupting control
circuit by above causes
Reset lockout by interrupting control at thermostat or main power
6. Interlock door switch open
Close access door or replace switch
7. Pressure switch not closing Perform following:
Ensure that unit is properly vented
Remove obstruction(s) from vent
Replace faulty tubing to pressure switch
8. Faulty pressure switch Replace pressure switch
9. Main valve not operating Perform following:
a) Defective valve If 24V power is measured at valve connections and valve remains closed,
replace valve
b) Loose wire connections Check and tighten all wiring connections
10. Integrated circuit board does not
power main valve
Perform following:
a) Loose wire connections Ensure that all wire connections are solid
b) Flame sensor grounded Ensure that flame sensor lead is not grounded or that sensor insulation or
ceramic is not cracked—replace as required
c) Incorrect gas pressure Supply pressure should be 5–14 IN WC for natural gas or 11–14 IN WC for
propane
d) Cracked ceramic at sensor Replace sensor
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