Lochinvar SNA400-125, SNA500-125, SNR200-100, SNA285-125 Sequence of operation, HTR Ignition

TM

Installation & Service Manual

11 Operating information (continued)

Sequence of operation

		OPERATION	DISPLAY
1.	When the tank temperature falls below the set point minus the		HTR: Standby
	differential, the control will start the burner.		TANK: 123.8F(129)
2. The control connects 120 VAC to the blower. The blower does not
	run at this time.		HTR: Standby
	•	The manual reset high limit must be closed before the control
		powers up the blower.	TANK: 123.8F(129)
	•	The control starts the internal pump.
	•	If there is an external limit connected to the heater, it must be
		closed.
3.	The control then starts a 10 second prepurge cycle.		HTR: PREPURGE
			TANK: 123.9F(129)
4.	Once the prepurge cycle is complete, and the blocked drain		HTR: IGNITION
	switch and auto-reset high limit are closed, the control starts the
	5 second trial for ignition by sending spark voltage to the spark		TANK: 123.9F(129)
	electrode and opening the gas valve.
5.	If the control does not detect flame by the end of the trial for		HTR: POSTPURGE, PREPURGE
	ignition, the control performs a 10 second postpurge, another
	prepurge and tries to light the burner again. If the burner does		TANK: 123.9F(129)
	not light after 4 trials, the control locks out for 1 hour and then
	tries another set of 4 trials.
6.	If the control detects a flame before the trial for ignition ends, it		HTR: RUN 20% RATE
	begins to modulate the burner in order to maintain the set point.		TANK: 124.8F(129)
7.	Once the tank temperature goes 3 - 4°F above the set point, the		HTR: POSTPURGE
	control will turn off the burner. The blower will remain on for the
	10 second postpurge cycle. The internal pump will continue to		TANK: 127.4F(129)
	run for its pump delay time, then turn off.
8.	Burner off.		HTR: Standby
			TANK: 124.7F(129)

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