A.O. Smith HYB-90N warranty Heat Cycle Definitions, State, Description

HEAT CYCLE DEFINITIONS

STATE	DESCRIPTION
Pre-purge	If the heat engine initial call-for-heat is successful (all checks are passed), the combustion fan
	is energized. The fan is started at a high speed for several seconds and the system verifies the
	fan speed. Input signals (from other parts of the water heater) are verified before completion of
	pre-purge including fan current verification. If one of the checks fails then the unit moves into
	the post-purge mode followed by the hard lockout mode and the appropriate error is displayed
	(see Error Code List and Clear-out Procedure).
Inter-Purge	If the flame presence is detected the control delays a pre-determined amount of time keeping
	the spark igniter energized. If flame presence is not detected within 5 seconds from the
	moment the gas was allowed in the combustion chamber (three ignition trials) then the control
	will initiate an ignition re-try for two more times. If flame presence cannot be verified within
	the given timing and after the ignitions’ re-try (if applicable), the system enters the post-purge
	mode and the gas flow is turned off.
Post-Purge	The heat engine gas valve is now turned off and the fan speed is changed to high speed for
	a predetermined time followed by a change of fan speed to a low value for the remaining
	duration of the post purge mode. The control will also verify that the proper conditions are
	maintained and there is no flame current sensed from the flame rod. If during the first stage
	of the post-purge mode (high speed fan operation) conditions for a new call for heat are met
	then the system will allow the state change to “Initial call for heat” only after the first stage of
	the post-purge mode is complete.
Standby Mode	After successful completion of post-purge, the fan is turned off and the control will wait until
	the determined conditions for a call for heat are met. In standby mode the unit continually
	monitors the input and output conditions and if abnormal conditions are detected the unit will
	enter in a lockout mode. If a call for heat is required and all checks are passed, the control
	will return to the initial call for heat state.
Lockout mode	This is a non-operational mode following the detection of an error in the system. In this stage
	the system displays an error message and continuously monitors input and output parameters.
	The system can move from this state into the stand-by mode only if the error is cleared (typical
	values for input and output parameters are recorded).
Proven Ignition	Once the power is turned on, the self-inspection is getting a normal status, water is turned
	on and fan’s current is normal then the ignition process will start for 5 seconds. If ignition is
	successful, the heater will go to normal combustion state and the ignition sparking will stop
	after 3 seconds. If ignition fails, the control will attempt to cycle through the heating stage
	three times and then attempt to re-ignite the gas. If ignition cannot be achieved, the control
	will end ignition attempts and prevent any more heating cycles, close the gas valve, turn the
	blower on, and display the E28 error message to the user.
	TABLE 2

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