Sequence Of Operation - Lochinvar Shield SNR150-100 Installation & Service Manual

10
Operating information

Sequence of operation

OPERATION
1. When the tank temperature falls below the set point minus the
differential, the control will start the burner.
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.
3. The control then starts the prepurge cycle.
4. Once the prepurge cycle is complete, and the blocked drain
switch and auto-reset high limit are closed, the control starts the
trial for ignition by sending spark voltage to the spark electrode
and opening the gas valve.
5. If the control does not detect flame by the end of the trial for
ignition, the control performs the 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.
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.
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
postpurge cycle. The internal pump will continue to run for its
pump delay time, then turn off.
8. Burner off.
TM
(continued)
HTR: Standby
TANK: 123.8F(129)
HTR: Standby
TANK: 123.8F(129)
HTR: PREPURGE
TANK: 123.9F(129)
HTR: IGNITION
TANK: 123.9F(129)
HTR: POSTPURGE, PREPURGE
TANK: 123.9F(129)
HTR: RUN 20% RATE
TANK: 124.8F(129)
HTR: POSTPURGE
TANK: 127.4F(129)
HTR: Standby
TANK: 124.7F(129)
Installation & Service Manual
DISPLAY
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