Lochinvar FTxl 400 Installation & Operation Manual page 68

11
Operating information
Sequence of operation
OPERATION
7. If fl ame is detected, it holds the fi ring rate steady for a few
seconds to let the fl ame stabilize, then it begins to modulate the
fi ring rate based on a set point or some other command (such as
a 0-10V BMS signal).
8. If the space heating call for heat is active, and the tank thermostat
or sensor starts a DHW call for heat, the boiler will switch to the
DHW mode. If programmed for normal DHW operation (not as a
zone), the DHW pump will turn on fi rst, then the boiler pump will
turn off (boiler and DHW pump operation briefl y overlap to ensure
fl ow is maintained through the unit). This will divert the boiler's
outlet water from the heating system and send it to the tank coil
instead. The control will then modulate to maintain the outlet
temperature to the DHW boiler set point.
9. If the boiler is not part of a Cascade, and both the space heating
and DHW calls for heat remain active long enough, the boiler will
switch back and forth between the two heating modes until one of
them is satisfi ed.
10. Once both calls for heat are satisfi ed, the control will turn off
the burner. The blower will continue to run during the postpurge
period.
11. Any pumps that are running will continue to run for their respective
pump delay times before turning off, unless programmed to
remain on continuously. A 60 second anti-cycle period will start,
which will delay any new call for heat until it times out.
12. In Standby, ready to start a new cycle.
68
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Installation & Operation Manual
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