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106308-05 - 3/23
APEX Installation, Operating, & Service Instructions
B. Troubleshooting when Help icon NOT flashing:
Indication Condition Possible Cause
Boiler not responding to
demand. Status and Priority
show
Standby.
Demand not
detected
• Boiler not seeing Enable/Disable or DHW Demand input. Check wiring
for loose connections or miswiring.
• If DHW Demand is expected, check that Domestic Hot Water
parameters are selected properly.
Boiler not responding to
demand. Status shows Standby
and Priority shows Central Heat
or Domestic Hot Water.
Boiler not
running,
pump(s)
running
Boiler not firing because temperature greater than Setpoint. Wait for
temperature to drop below Setpoint minus Differential Below or adjust
Setpoint as needed.
Boiler running but System Pump
or Boiler Pump is not running
Pump(s) not
running
• Check wiring for loose connections or miswiring.
• When there is DHW Demand: Boiler Pump will be off if set to Central
Heat, Off DHW Demand and System Pump will be off if set to Central
Heat, Optional Priority. This feature allows for fast indirect water heater
recovery. After Priority Time has expired or DHW Demand ends, Boiler
Pump and System Pump are free to run for Enable/Disable demand.
Display completely dark, fan off,
LWCO lights off, no green power
light on boiler control
No 120 VAC
power at boiler
Circuit breaker tripped. Check breaker and wiring between breaker and
boiler.
Display completely dark, green
power light illuminated on boiler
control
No 24VDC
power at
display
• Loose 120 VAC wiring connection between J-box and display power
supply.
• Loose 24VDC wiring connection between power supply and display.
Display blank with “Reading”
shown
Display lost
communication
with control
Failure to establish communication upon display boot-up. After
establishing communication, reboot display to read controller and setup
display properly.
Communication Error 2
Communication
Fault
The display write attempt has failed.
• Password level is too low for parameter being changed
• Boiler control is un-configured or has a memory failure. Lockout 20
Safety Data Verification will be displayed if control is not configured or
has had a memory loss. In this case replace control.
Communication Error 3
Communication
Fault
Display has lost communication with control.
If no green power light on control, check for:
• Blown 24V fuse on low voltage PCB. Check for 24V shorts before
replacing fuse.
• Loose or defective wiring between transformer and control.
• Bad transformer
If green power light is illuminated on control, check for:
• Loose or defective wiring between display and control
• Defective display
• Defective control
• Incorrect COM Port parameters. Refer to EMS Modbus Parameters in
Parameter Adjustment section.
Blinking green power light on
boiler control
Control Fault
The green light is connected to internal power supply. The power supply is
repeatedly starting and stopping (not normal) making the light flash. The
microprocessors are not running. Try disconnecting all terminals except 24
VAC to power the control. The green light should be steady. If it is not, then
the control is defective. If steady, start plugging in all the connectors while
watching the green light. When faulty wiring is reconnected, green light will
begin to flash.
12 Troubleshooting (continued)
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