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106308-05 - 3/23
APEX Installation, Operating, & Service Instructions APEX Installation, Operating, & Service Instructions
Lockout
Number
Condition Possible Cause
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
42
AC Phase Fault
AC inputs phase reversed
• Check control and display connections.
• Verify line voltage frequency and voltage meet specifications.
• Verify 24 VAC transformer functioning properly.
47
Flame Lost
Flame lost at some stage. See
display for details.
• Gas pressure too low. See minimum on boiler rating label.
• Air-fuel mixture out of adjustment. See System Start-up Section.
• Disconnected or defective flame sensor wire.
• Defective flame sensor.
• Defective gas valve. Before replacing valve, check for 24 VAC at
gas valve connector during trial for ignition.
284
Memory Reset To
Default
OEM Memory Lost, Honeywell
Default Memory Restored
• Control failure
• Consult factory
• Replace control
Table 12-5: Hard Lockout Codes (continued)
12 Troubleshooting (continued)
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