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HL2
Series
This heater must be installed and serviced by trained gas installation and service
personnel only.
Do not bypass any safety features or the heater's built in safety mechanisms will be
compromised.
Sequence of Operation
Standby: The MICRO 60U-24 CONTROL continually checks for internal faults, circuit integrity and relay
contact positioning.
Starting Circuit: Upon a call for heat, the control verifies that the differential switch is in the proper
position (open). The control energizes the fan. Once operational static pressure is achieved, the
differential switch will close initiating the ignition sequence. The glo-bar is powered and the gas
valve opens after 45 seconds. If the flame is not sensed, the heater will attempt to re-ignite for a total
of three (3) trials for ignition before proceeding to soft lockout.
Single Stage Running Circuit: After ignition, the flame rod monitors burner flame. If sense of flame is
lost, the control closes the gas valve within one second and a new trial sequence (identical to the
starting sequence) is initiated. If flame sense is not established within 8.5 seconds, the heater will
attempt two (2) additional ignition sequences before proceeding to soft lockout. The control can be
reset by briefly interrupting the power source.
Two Stage Running Circuit: The second stage on the gas valve is powered directly from the second
stage of the thermostat. In order for two stage to flow to a higher output, single stage must be
energized as well. The thermostat determines which stage to maintain for the desired comfort level.
Shut Down: When the thermostat is satisfied, the fan will enter a two (2) minute post-purge cycle. Refer
to page 54 for diagnostics; soft & hard lockout.
!
WARNING
53
4.0
Operation
•
Sequence of Operation
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