MAINTENANCE—CONTINUED
Vent Temperature Limit Switch Maintenance
The vent temperature limit switch (see Figure 33) is located on the discharge of the combustion air blower (venter)
and its purpose is to prevent the vent gas temperature from exceeding a temperature that will harm the PVC vent
pipe. If the vent temperature limit switch is activated, the cause must be determined and corrected before the heater
is placed back into operation. Activation of the manually reset vent temperature limit switch could be caused by one
or more of the following:
• Manifold gas pressure too high
• Heat content of fuel being burned is too high
• Reduced circulating airflow due to dirty and/or plugged air moving components
• Excess dirt on heat exchanger(s)
• Failed heat exchanger(s)
After the cause is determined and corrected, press the red button on the switch to reset it.
Disconnect Switch Replacement
The disconnect switch (see Figure 33) is located in the sealed electrical box inside the control compartment with the
toggle on the rear of the heater. If it is determined that the disconnect switch 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, inlet air guard or inlet air cap, and the vent terminal cap. Clean all openings and replace any defective parts.
Condensate Drain System
Check the condensate disposal system annually. Remove the condensate traps and flush them with clear tap water
to remove any sediment that may have accumulated. Check to be ensure that the piping to the sanitary drain has
not been damaged. Check the sanitary drain to verify that it flows freely.
TROUBLESHOOTING
Unit Troubleshooting Using DSI Control Module
The SSD on the DSI control module (refer to Circuit Board (DSI Control Module) section) may be used to troubleshoot
the unit. The control module monitors the operation of the heater, and the display indicates normal operation and
various abnormal conditions. If the heater fails to operate properly, check this display to determine the cause and/or
to eliminate certain causes. See Figure 34 for a flowchart for troubleshooting the unit using the DSI control module.
NOTES:
• If troubleshooting indicates that repair of the DSI control module is required, note that its only
replaceable part is the fuse (see Figure 24), which is a type ATC or ATO 3A fuse, color code violet
(PN 201685).
• IMPORTANT: When using a multimeter to troubleshoot the 24V circuit, place the multimeter’s test
leads into the connectors located on the ignition control. Do not remove connectors or terminals
from the electrical components. Doing so can result in misinterpreted readings caused by the
control module’s fault mode monitoring circuits.
54
I-UEZ (04-21) 1034347-0
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