Thermal Solutions APEX APX425C - Page 124

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106308-05 - 3/23
APEX Installation, Operating, & Service Instructions
Lockout
Number
Condition Possible Cause
7
Return Sensor
Fault
Shorted or open return temperature
sensor.
• Shorted or miswired return sensor wiring
• Defective return sensor
8
Supply Sensor
Fault
Shorted or open supply
temperature sensor.
• Shorted or miswired supply sensor wiring
• Defective supply sensor
9
DHW Sensor
Fault
Shorted or open Domestic Hot
Water (DHW) temperature sensor.
• Shorted or miswired DHW sensor wiring
• Defective DHW sensor
10
Stack Sensor
Fault
Shorted or open flue gas (stack)
temperature sensor.
• Shorted or miswired flue sensor wiring
• Defective flue sensor
13
Flame rod
shorted to ground
Flame rod shorted to ground
• Shorted or miswired flame rod wiring
• Defective flame rod
14
Delta T Inlet/
Outlet High
Temperature rise between supply
and return is too high.
Inadequate boiler water flow.
• Boiler pump not operating
• Boiler pump undersized
• Valve closed
15
Return
Temperature
Higher Than
Supply
Return temperature was greater
than supply temperature for at least
75 seconds.
• Reversed flow through boiler. Verify correct piping and circulator
orientation.
• No boiler water flow. Verify system is purged of air and
appropriate valves are open.
• Defective supply or return sensor
16
Supply
Temperature
Risen Too Quickly
Supply water temperature has risen
too quickly.
Inadequate boiler water flow. See also causes for Hard Lockout 4.
• Boiler pump not operating
• Boiler pump undersized
• Valve closed
17
Fan Speed Not
Proved
Normal waiting for blower speed to
match purge and light-off setpoint.
N/A
27
Interrupted
Airflow
Switch (IAS) ON
Air proving switch failed to open.
Air proving switch closed before Prepurge.
• Failed air proving switch. Check switch for proper operation.
• Short in limit string wiring
27
Interrupted
Airflow Switch
(IAS) OFF
Air proving switch failed to close.
Air proving switch open during Prepurge or Drive Lightoff.
• Check for vent or combustion air pipe blockage.
• Confirm air proving switch hose connected to gas valve outlet
tapping and outlet tapping internal screw is open.
• Loose or defective limit string wiring
Table 12-3: Soft Lockout (Hold) Codes (continued)
12 Troubleshooting (continued)