Applied Air GAS-FIRED HEATERS, Installation & Operation Instruction

Page: 23 / 64

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Modulating Operation
Set high fi re by adjusting main gas regulator and by the
high fi re adjusting screw on the butterfl y valve.
Observe fl ame as burner modulates when thermostats
are adjusted.
NOTE: Flame should modulate slowly and evenly
throughout the entire travel, although fl ame may
become somewhat “dirty” during travel. If stopped
at any point, proper combustion should resume.
Turn all modulating thermostats to their lowest setting
without turning the burner off, or with power off remove
the coil wire on low fi re hold relay and restart burner.
Set low fi re with the low fi re adjusting screw on the
butterfl y valve.
Observe low fi re, it should be substantial enough to
maintain proper combustion and be within the designed
turndown range of the burner.
CAUTION: Too low of an input setting will cause
condensation of the fl ue gases, this should be
avoided unless condensate drains are provided.
See following drawings for operation of modulating
thermostat and typical circuit. SW-11/SW-13 should
cycle the burner.
See fi nal checks and adjustments toward the end of
this section.
C000723