7
2.3
SEQUENCE OF OPERATION
OPERATION
DISPLAY
1.
Upon a call for heat, the control turns on the appropriate
pumps.
WHR: Standby
OUT: 61.4C
2.
The control connects 230 VAC to the fan. The fan does
not run at this time.
If the unit is equipped with a flow switch or low
water cut-off, it must close before the control
powers up the fan.
If the unit is equipped with a manual reset high
limit it must be closed before the control powers
up the fan.
If the unit is equipped with a solenoid valve and/or
a vent valve, they will be energized along with the
fan.
If the unit is equipped with a gas pressure switch,
it must close at this time.
If there is an auxiliary device connected to the
unit, the unit will then provide 24 VAC to its enable
relay. If the auxiliary device has a proving switch,
it must close before the sequence continues.
WHR: Standby
OUT: 61.4C
3.
The control then starts a 10 second prepurge cycle.
WHR: PREPURGE
OUT: 61.5C
4.
Once the prepurge cycle is complete, and the blocked
drain 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.
WHR: IGNITION
OUT: 61.5C
5.
If the control does not detect flame by the end of the
trial for ignition, the control performs a 10 second
postpurge. On the SHW45-325CE to SHW115-435CE
models, the control will perform another prepurge and
will try to light the burner again. If the burner does not
light after 4 trials, the control will lockout for 1 hour and
then try another set of 4 trials. On the SHW145-435CE
the unit will lockout until manually reset.
WHR: POSTPURGE, PREPURGE
OUT: 61.5C
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.
WHR: RUN 20% RATE
OUT: 62.6C
7.
Once the call for heat is satisfied, the control will turn off
the burner. The fan will remain on for the 10-second
postpurge cycle. The primary pump will continue to run
for its respective pump delay time, and then turn off.
WHR: POSTPURGE
OUT: 64.5C
8.
Primary pump switches off.
WHR: Standby
OUT: 64.8C
