Lochinvar KNIGHT 81-286 Service Manual page 11

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Service Service
(continued)
Table 1-1 Sequence of Operation
OPERATION
1. Upon a call for heat, the gas pressure switch(es) must be closed.
2. Once the gas pressure switch(es) are closed, the control turns
on the appropriate pumps (system and boiler pumps for space
heating, DHW pump for DHW). The flow switch and/or LWCO
must close.
3. The control turns on power to the louver relay. The louver
proving switch, air pressure switch, and blocked drain switch
must close.
4. The control starts a 15 second prepurge cycle by initiating the
blower.
5. The control starts a 4 second trial for ignition by firing the spark
electrode and opening the gas valve.
6. If flame is not detected within 1 second after the sparking ends,
the control will perform a 10 second post-purge, then start
another prepurge cycle and try to light the burner again. The
control will perform a total of 4 attempts before locking out.
7. If flame is detected, it holds the firing rate steady for 5 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).
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