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4.0
Operation
•
Sequence of Operation
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 ignition module (circuit board)continually checks for internal faults, circuit integrity and relay
contact positioning.
Starting Circuit: Upon a call for heat, the control verifies that the burner and exhaust pressure switches
are in their proper positions. The control energizes the fan. Once operational static pressure is
achieved, the burner pressure switch will close initiating the ignition sequence. The hot surface
igniter 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 3 trials for ignition before proceeding to soft lockout.
Low Fire 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 additional ignition sequences before proceeding to soft lockout. The control can be reset by
briefly interrupting the power source.
High Fire Running Circuit: The second stage on the gas valve is powered directly from the second
stage of the thermostat. In order for high fire to engage, low fire 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.
Diagnostics
Lockout:
The controls will automatically lockout the heater system when an external or system fault occurs. There
are two types of lockout:
Soft Lockout: The heater will attempt to light three times. In the event of a failed attempt to light, (gas
pressure, valve, no flame sense etc.), the heater will enter a soft lockout period for 30
minutes and then attempt to light three more times before entering hard lockout mode.
Hard Lockout: If proof of flame is not established, a component failure occurs or blockages are evident,
the heater will enter a hard lockout. If lockout occurs, the control can be reset by briefly
interrupting the power source. Refer to Chart 4.1 for a description of LED codes.
Internally located operational indicator lights are provided to assist in troubleshooting of the heater. Refer
to pages 44-47 for additional troubleshooting.
•
Diagnostics
WARNING
!
40
DST
Series
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