Detroit Radiant Products Company UH Series - Manual (Page 43)

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UH Series 4.0 Operation • Sequence of Operation
4.0 Operation
WARNING
!
This appliance does not have a pilot ignition. It is equipped with an ignition device
which automatically lights the burner.
Do not attempt to light the system by hand.
WARNING
!
Use only your hand to turn the manual shut off. Never use tools. If the
knob will not turn by hand, don’t try to repair it; call a qualified technician.
Force or attempted repair may result in a fire or explosion.
Sequence of Operation
Standby: The ignition control continually checks for internal faults, circuit integrity and relay contact
positioning. The LED is lit indicating power is applied.
Starting Circuit: Upon a call for heat, the control verifies that the limit switch is closed and the
differential pressure switch is in the open position. The control energizes the induced draft motor. Once
operational static pressure is achieved the differential switch will close initiating the ignition sequence.
The control energizes the spark and main gas valve for 10 seconds. If the flame is not sensed, the
control will attempt to re-ignite for a total of (3) tries for ignition before proceeding to soft lockout.
Running Circuit: After ignition, the flame rod monitors burner flame. If flame sense is not established
within 10 seconds, the control will attempt two (2) additional ignition sequences before proceeding to
soft lockout. The control can be reset by briefly interrupting the power source. If flame is sensed the
control waits for a 30 second heat blower on delay and then energizes the indoor blower, the control
proceeds to steady heat mode. If sense of flame is lost, the control closes the gas valve within 1
second and a new trial sequence (identical to the starting sequence) is initiated.
Shut Down: When the thermostat is satisfied, the control closes the valve and the induced draft motor
remains on for a 5 second post-purge period. The indoor blower is de-energized after 120 seconds.