Installation & Operation Manual
62
11
Operating information
Sequence of operation
OPERATION
DISPLAY
1. The control will turn on the water heater pump (always ON except
in Night Setback). The flow switch and/or LWCO must close.
2. The control turns on power to the louver relay. The louver proving
switch, air pressure switch, and blocked drain switch must close.
3. The control starts the prepurge cycle.
4. The control starts the trial for ignition by firing the spark
electrode and opening the gas valve.
5. If flame is not detected after the sparking ends, the control will
perform a postpurge, then start another prepurge cycle and try
to light the burner again. On the 501 and larger models, the control
will lock out if this second attempt also fails. On the 400 and
smaller models, the control will perform a total of 4 attempts before
locking out.
6. If flame is detected, it holds the firing rate steady for a few seconds
to let the flame stabilize, then it begins to modulate the firing rate
based on a set point or some other command (such as a 0-10V
BMS
signal).
7. Once the call for heat is satisfied, the control will turn off the
burner. The blower will continue to run during the postpurge.
8. The water heater pump will continue to run for its respective
pump delay time before turning off. A 60 second anti-cycle period
will start, which will delay any new call for heat until it times out.
9. In Standby, ready to start a new cycle.
