Chapter 5 Adjustment Procedures
5-6 750-177
I. MODULATING TEMPERATURE
CONTROL (Hot Water)
Figure 5-3: Hot Water Controls
Turn the knob on the front of the case until the
pointer indicates the desired setpoint temperature.
The desired set point is the center point of a
proportional range. The control has a 3 to 30
differential and may be adjusted to vary the
temperature range within which modulating action is
desired. With the cover off, turn the adjustment
wheel until pointer indicates desired range.
To prevent burner shutdown at other than low-
fire setting adjust modulating temperature con
-
trol to modulate low fire BEFORE operating limit
te
mperature control shuts off burner. Failure to
follow these instructions could result in dam-
age to the equipment.
J. OPERATING LIMIT TEMPERATURE CONTROL (Hot Water)
Set “cut-out” (burner off) temperature on the scale by inserting a screwdriver through the cover opening to
engage the slotted head adjusting screw. The “cut-in” (burner on) temperature is the cut-out temperature
MINUS the differential. The differential is adjusted from 5 to 30° F.
K. HIGH LIMIT TEMPERATURE CONTROL (Hot Water)
Set the “cut-out” (burner off) temperature on scale using the adjusting screw. The control will break the circuit
and
lock out on a rise in water temperature above the setting. The setting should be sufficiently above the
operating limit temperature to avoid unnecessary shutdowns. The control requires manual resetting after
tripping on a temperature increase. To reset, allow the water temperature to drop below the cut-out setting
less differential, and then press the manual reset button.
L. LOW WATER CUTOFF DEVICES (Steam and Hot Water)
No adjustment is required since LWCO controls are preset by the original manufacturer. However, if the water
level is not maintained, inspect the devices immediately and replace as required.
M. COMBUSTION AIR PROVING SWITCH
Air pressure against the diaphragm actuates the switch which, when made, completes a circuit to prove the
presence of combustion air. Since the pressure of the combustion air is at its minimum value when the damper
is full closed, the switch should be adjusted under that situation. It should be set slightly below the minimum
pressure, but not too close to that point to cause nuisance shutdowns.
The run/test switch on the program relay should be set to TEST. T
urn the burner switch on. The blower will
start (provided that all limit circuits are completed) and the programmer will remain in the low-fire (damper
closed) portion of the prepurge.
Slowly turn down the air switch adjusting screw until it breaks the circuit. Here the
programmer will lock out
and must be manually reset before it can be restarted. Add a half turn or so to the adjusting screw to remake
its circuit.
Recycle the program relay to be sure that normal operation is obtained. R
eturn the test switch to the RUN
position.
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