Form I-UDB, P/N 202658 R10, Page 41
General Troubleshooting
PROBLEM
PROBABLE CAUSE
REMEDY
Venter motor will not
start
1. No power to unit.
1. Turn on power; check supply fuses or main circuit breaker. Turn on built-in control switch (Model UDBS
only); replace switch if not operating.
2. No 24 volt power to integrated circuit
board.
2. Turn up thermostat; check control transformer output.
3. Integrated circuit board fuse blown.
3. Correct cause. Replace fuse (type ATC or ATO, 32VDC, 3A).
4. No power to venter motor.
4. Tighten connections at circuit board and/or motor terminals.
5. Integrated circuit board defective.
5. Replace integrated circuit board.
6. Defective venter motor.
6. Replace venter motor. See Paragraph 10.2.5.
Burner will not light
1. Manual valve not open.
1. Open manual valve.
2. Air in the gas line.
2. Bleed gas line (initial startup only).
3. Gas pressure too high or too low.
3. Supply pressure should be 5-14" w.c. for natural gas or 11-14" w.c. for propane.
4. No Spark:
4.
a) Loose wire connections.
a) Be certain all wire connections are solid.
b) Transformer failure.
b) Be sure 24 volts is available.
c) Incorrect spark gap.
c) Maintain spark gap at 1/8".
d) Spark cable shorted to ground.
d) Replace worn or grounded spark cable.
e) Spark electrode shorted to ground.
e) Replace if ceramic spark electrode is cracked or grounded.
f) Burner not grounded.
f) Make certain integrated circuit board is grounded to ignitor.
g) Circuit board not grounded.
g) Make certain integrated circuit board is grounded to furnace chassis.
h) Unit not properly grounded.
h) Make certain unit is properly field grounded to earth ground and properly phased (L1 to hot lead L2 to neu-
tral).
i) Integrated circuit board fuse blown.
i) Correct cause. Replace fuse (type ATC or ATO, 32VDC, 3A).
j) Faulty integrated circuit board.
j) If 24 volt is available to the integrated circuit board and all other causes have been eliminated, replace board.
5. Lockout device interrupting control circuit
by above causes.
5. Reset lockout by interrupting control at the thermostat or main power.
6. Interlock door switch open (UDBS only).
6. Close access door or replace switch.
7. Combustion air proving switch not closing 7. a) Make sure unit is properly vented.
b) Remove obstructions from vent.
c) Replace faulty tubing to pressure switch.
8. Faulty combustion air proving switch.
8. Replace combustion air proving switch.
9. Main valve not operating.
9.
a) Defective valve.
a) If 24 volt is measured at the valve connections and valve remains closed, replace valve.
b) Loose wire connections
b) Check and tighten all wiring connections.
10. Integrated circuit board does not power
valve.
10.
a) Loose wire connections.
a) Check and tighten all wiring connections.
b) Flame sensor grounded.
b) Be certain flame sensor lead is not grounded or insulation or ceramic is not cracked. Replace as required.
c) Incorrect gas pressure.
c) Supply pressure should be 5-14" w.c. for natural gas or 11-14" w.c. for propane.
d) Cracked ceramic at sensor.
d) Replace sensor.
Burner cycles on
and off
1. Gas pressure too high or too low.
1. Supply pressure should be 5-14" w.c. for natural gas or 11-14" w.c. for propane.
2. Burner not grounded
2. Make certain integrated circuit board is grounded to ignitor.
3. Circuit board not grounded.
3. Make certain integrated circuit board is grounded to furnace chassis.
4. Faulty integrated circuit board
4. If 24 volt is available to the integrated circuit board and all other causes have been eliminated, replace
board.
5. Combustion air proving switch not closing. 5. a) Make sure unit is properly vented.
b) Remove obstructions from vent.
c) Replace faulty tubing to pressure switch.
6. Faulty combustion air proving switch.
6. Replace combustion air proving switch.
7. Flame sensor grounded.
7. Be certain flame sensor lead is not grounded or insulation or ceramic is not cracked. Replace as required.
8. Cracked ceramic at sensor.
8. Replace sensor.
9. Incorrect polarity.
9. Reverse line volt leads to integrated circuit board.
10. Pin terminal loose at 9-pin plug.
10. Replace wire harness.
No heat (Heater Oper-
ating)
1. Incorrect valve outlet pressure or orifice. 1. Check valve outlet pressure. See Rating plate for manifold pressure.
2. Cycling on limit control.
2. Check air throughput.
3. Improper thermostat location or adjust-
ment.
3. See thermostat manufacturer's instructions.
Blower motor or venter
motor will not run
1. Circuit open.
1. Check wiring and connections.
2. Defective integrated circuit board.
2. Replace board.
3. Defective motor or starter.
3. Replace motor or starter.
Blower or venter motor
turns on and off while
burner is operating
1. Motor overload device cycling on and off. 1. Check motor load against motor rating plate. Replace motor if needed.
Blower motor or ven-
ter motor cuts out on
overload
1. Low or high voltage supply.
1. Correct electric supply.
2. Defective motor.
2. Replace motor.
3. Poor air flow.
3. Clean motor, blower, blower guard, filter, and coils.
4. Defective bearing or lubrication.
4. Lubricate bearings (motor permitting) or replace motor.
Blower motor cuts out
on overload
1. Improper motor pulley and/or adjustment. 1. See instructions in Paragraph 6.4.2.
2. Improper static pressure in the duct
system.
2. Adjust duct system dampers.
3. Low voltage.
3. Check power supply.
