Robur GAHP Line AR Series, Installation, Use And Maintenance Manual, Page: 92 / 100

Appendix
Ed. 2014-08
89
APPENDIX
IGNITION CONTROL BOX
When power is supplied to the unit (to the “R” terminal on the ignition control box), ignition
control will reset, perform a self check routine, flash the diagnostic LED, and enter
thermostat scan state.
When the control switch is closed, the electronic control board will energize the ignition
control box starting the ignition sequence (24 volts applied to the “W” terminal on the
ignition box).
The ignition control box will check the differential air pressure switch for open contacts.
•
If the differential air pressure switch contacts are closed and stay closed for 30
seconds, an air flow fault will appear. The diagnostic LED on the ignition control box
indicates this fault. In this mode, the ignition control box pre-mixer blower will not
start.
If the pressure switch contacts are open, the ignition control box pre-mixer blower will
instead start.
•
An air flow fault will occur if the air pressure switch contacts remain opened for 30
seconds after the pre-mixer blower start. The diagnostic LED on the ignition control
box indicates this fault. In this mode, the ignition control box will keep the pre-mixer
blower energized.
If the air pressure switch contacts close after the pre-mixer blower starts (normal
operation), a pre-purge delay begins and the ignition sequence continues.
Next, the ignition control box energizes an ignition transformer that generates a high
intensity spark at the igniter to ignite the gas/air mixture. Simultaneously, the gas valve is
energized, allowing the flow of gas to the burner.
As soon as the ignition period ends, the flame sensor checks for flame presence. If the
flame is detected, the gas valve and pre-mixer blower remain energized.
Should the burner fail to light, flame is not detected during the first trial for ignition: the gas
valve and ignition transformer are de-energized and the ignition control box begins an
inter-purge delay before another ignition attempt. The control will attempt two additional
ignition trials (total of 3 ignition trials) before going into lockout. In lockout, the gas valve
will de-energize immediately and the pre-mixer blower will turn off. Ignition control box
requests a reset operation to restart.
The thermostat (“W” terminal), air pressure switch and burner flame are constantly
monitored to assure proper system operation. When the call for heat has ended (24volts
removed from “W” terminal on ignition control), the gas valve is de-energized immediately.
The ignition control then senses loss of flame and de-energizes the pre-mixer blower.
To reset the ignition box, see related procedure in paragraph “RESET OPERATIONS
AND MANUAL DEFROSTING COMMAND”, on page 21.