CONTROL PANEL OPERATING PROCEDURES
3-8
3.8. START SEQUENCE
When the Control Box
ON/OFF
switch is set to
the
ON
position, it checks all pre-purge safety
switches to ensure they are closed. These
switches include:
•
Safety Shut-Off Valve Proof of Closure
(POC) switch
•
Low Water Level switch
•
High Water Temperature switch
•
High Gas Pressure switch
•
Low Gas Pressure switch
If all of the above switches are closed, the
READY
light above the
ON/OFF
switch will light
and the unit will be in the Standby mode.
When there is a demand for heat (hot water), the
following events will occur:
NOTE:
If any of the Pre-Purge safety device switches
are open, the appropriate fault message will be
displayed. Also, the appropriate fault messages
will be displayed throughout the start sequence,
if the required conditions are not observed.
1. The
DEMAND
LED status indicator will light.
2. The unit checks to ensure that the proof of
closure switch in the Safety Shut-Off Valve
(SSOV) is closed (Figure 3-3).
Figure 3-3.
Safety Shut-Off Valve
3. With all required safety switches closed, a
purge cycle will be initiated and the following
events will occur:
(a) Blower relay energizes and turns on
blower.
(b) Air/Fuel Valve rotates to the full-open
purge position and closes the purge
position switch. The dial on the Air/Fuel
Valve (Figure 3-4) will read 100 to
indicate that the valve is full-open
(100%).
STEPPER
MOTOR
DETAIL "A"
DIAL
(DETAIL “A”)
100
B
LO
W
E
R
B
U
R
N
E
R
Figure 3-4.
Air/Fuel Valve In Purge Position
4. The blower proof switch (Figure 3-5) closes;
the display shows
Purging
and indicates the
elapsed time of the purge cycle in seconds.
