Crown Boiler BWF Series Installation Instructions Manual page 44

12. Operation (continued)
E. Safety Control Operation
Air Pressure Switch (APS) - The APS proves that
the fan is running before allowing the ignition
sequence to proceed. Failure of this switch to
close is usually the result of a problem with the
vent system, such as a blockage, or a problem
with the fan. If this switch must be replaced, it
must be replaced with an identical switch or one
that is shown in this documentation as being a
suitable replacement for this boiler (see Parts
Section of boiler installation manual).
IDL 1200 Low Water Cut Off- The IDL 1200
Low Water Cut-Off is designed to protect from
potentially damaging low water conditions in the
boiler. In the event of a low water condition, the
"LOW WATER" LED will turn on and the control will
shutdown the burner.
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