UDX Installation Manual

45
UBX-UBZ-UDX-UDZ-IOM (03-22) 1034344-C
Table 24. General Troubleshooting
Symptom Probable Cause Remedy
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
Burner
cycles ON
and OFF
1. 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
2. Burner not grounded Ensure that integrated circuit board is grounded (terminals P1–1)
3. Circuit board not grounded Ensure that integrated circuit board is grounded to furnace chassis
4. Faulty integrated circuit board If 24V power is available to integrated circuit board and all other causes have
been eliminated, replace board
5. Pressure switch not closing Perform following:
Ensure that unit is properly vented
Remove obstruction(s) from vent
Replace faulty tubing to pressure switch
6. Faulty pressure switch Replace pressure switch
7. Flame sensor grounded Ensure that flame sensor lead is not grounded or that sensor insulation or
ceramic is not cracked—replace as required
8. Cracked ceramic at sensor Replace sensor
9. Incorrect polarity Reverse line volt leads to integrated circuit board
10. Pin terminal loose on wire harness Replace wire harness
No heat
(heater
operating)
1. Incorrect valve outlet pressure or orifice Check valve outlet pressure (refer to unit rating plate for manifold pressure)
2. Cycling on limit control Check air throughput
3. Improper thermostat location or
adjustment
Refer to thermostat manufacturer's instructions
Fan or
venter
motor will
not run
1. Circuit open Check wiring and connections
2. Defective integrated circuit board Replace board
3. Defective motor Replace motor
—Continued