Lochinvar Shield SNA285-125 - Manual (Page 49)

49
11
Operating information
(continued)
OPERATION DISPLAY
1. When the tank temperature falls below the set point minus the
differential, the control will start the burner.
HTR: Standby
TANK: 123.8F(129)
2. The control connects 120 VAC to the blower. The blower does not
run at this time.
• The manual reset high limit must be closed before the control
powers up the blower.
• The control starts the internal pump.
• If there is an external limit connected to the heater, it must be
closed.
HTR: Standby
TANK: 123.8F(129)
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
switch and auto-reset high limit are closed, the control starts the
5 second trial for ignition by sending spark voltage to the spark
electrode and opening the gas valve.
HTR: IGNITION
TANK: 123.9F(129)
5. If the control does not detect flame by the end of the trial for
ignition, the control performs a 10 second postpurge, another
prepurge and tries to light the burner again. If the burner does
not light after 4 trials, the control locks out for 1 hour and then
tries another set of 4 trials.
HTR: POSTPURGE, PREPURGE
TANK: 123.9F(129)
6. If the control detects a flame before the trial for ignition ends, it
begins to modulate the burner in order to maintain the set point.
HTR: RUN 20% RATE
TANK: 124.8F(129)
7. Once the tank temperature goes 3 - 4°F above the set point, the
control will turn off the burner. The blower will remain on for the
10 second postpurge cycle. The internal pump will continue to
run for its pump delay time, then turn off.
HTR: POSTPURGE
TANK: 127.4F(129)
8. Burner off.
HTR: Standby
TANK: 124.7F(129)
Sequence of operation
Installation & Service Manual TM