Thermal Solutions APEX APX425C Installation, Operating And Service Instructions page 128

12
Troubleshooting
E. Limit String Status
From the Help Menu, select Limit String Status to view status of individual safety limits. See Figure 12-6. ON
indicates closed limit contact. OFF with red background indicates open limit contact. When a limit is OFF, all
limits connected to the same control terminal (e.g. A2) and will show OFF. Limits downstream (below) the OFF
limit and connected to a different control terminal may also show OFF. When troubleshooting, check OFF limits in
order from top to bottom to isolate the problem. Air proving switch and flow switch limits cycle normally based on
function of boiler. Refer to Figure 8-5, Ladder Diagram for limit string details.
Control Terminal
F. Sensor Status
Select Sensor Status from the Help Menu or Sensors from the Main Menu to view status of individual sensors.
Select an individual sensor to display gauge reading on right side of display. A failed sensor is shown with a red
background as in Figure 12-7. See Table 12-8 for sensor fault diagnostic help and Tables 12-9 through 12-12 for
sensor temperature versus resistance values.
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(continued)
Figure 12-6: Limit String Status
Figure 12-7: Sensors Screen with Shorted Supply Sensor
APEX Installation, Operating, & Service Instructions
106308-05 - 3/23