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UBX-UBZ-UDX-UDZ-IOM (07-23) 1034344-K
MAINTENANCE—CONTINUED
Maintenance Procedures—Continued
Flame Rollout Switch Maintenance (Models UDX and UDZ Unit Sizes 030–125 Only)
• The cause of a flame rollout switch (see Figure 19) activating must be determined. Activation of the manually-reset
flame rollout switch could be caused by one or more of the following:
a. Restricted or plugged heat exchanger
b. Too much building exhaust
c. Manifold gas pressure too high
d. Restricted combustion air inlet or exhaust outlet in combination with defective pressure switch
e. Electrical power interruption during operation
f. Unit being operated with line voltage disconnect (24V thermostat is required)
• If a flame rollout switch trips, inspect the burner/control compartment for signs of excessive heat and burned wiring.
If there is damage to the control compartment, repairs must be made before resetting the switch.
• If the compartment appears normal, reset by depressing the red button on the switch (15–20 minutes are required
for the switch to cool sufficiently before resetting). A distinct click will be felt when the switch resets. Operate the
furnace. If the flame rollout switch trips again, determine and correct the cause before resetting the switch.
• If it is determined that the flame rollout switch needs replacing, use only the factory-authorized replacement part
that is designed for that size of heater. The disconnect toggle switch is on the rear of the heater.
Transformer Maintenance
Use a voltmeter to verify that there are 24V output from the transformer (see Figure 19). If the transformer is not
functioning, it must be replaced. Use a replacement transformer identical to the factory-installed model. For the
transformer location, see Figure 11.
Disconnect Switch Replacement (Models UBZ and UDZ Only)
If it is determined that the disconnect switch (see Figure 19) needs replacing, use only the factory-authorized
replacement part that is designed for the heater. Always replace the electrical box cover.
Vent or Vent/Combustion Air System Maintenance
Check the complete system at least once a year. Inspection should include all joints, seams, concentric adapter box
(models UBZ and UDZ), inlet air guard or inlet air cap (models UBZ and UDZ), and the vent terminal cap. Clean all
openings and replace any defective parts.
TROUBLESHOOTING
General Troubleshooting
Table 19. General Troubleshooting
Symptom Probable Cause Remedy
A. 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)
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