Burnham MPO Series, Installation & Service Instructions Manual

Page: 36 / 64

36
D. ADJUST CONTROL SETTINGS with burner
service switch turned “ON” and room thermostat set
10°
below room temperature.
1. Adjustment and display modes of the L7248C Oil
Electronic Aquastat Controller.
a. On the L7248C, the overall range of the High
Limit is from 180°F to 240°F (82°C to 116°C).
b. Set the High Limit (designated HL) on the
L7248C Aquastat Control at 180°F. This
temperature setting may be varied to suit
requirements of installation. Differential is fi xed
at 15°F.
i. Adjusting Settings:
To discourage unauthorized changing of
Aquastat settings, a procedure to enter the
adjustment mode is required. To enter the
adjustment mode, press the
UP, DOWN,
and I buttons (see Figure 23) simultaneously
for three (3) seconds. Press the ‘I’ button
until the feature requiring adjustment is
displayed:
·
High Limit
·
°F -- °C (Toggle)
Then press the UP and/or DOWN buttons
to move the set point to the desired value.
After 60 seconds without any button inputs,
the control will automatically return to the
READ mode.
Figure 23: L7248C Circuit Board Layout -
Horizontal Mount
ii. Display:
In the RUN mode, the Aquastat will fl ash
“bt” (boiler temp.) followed by the temp-
erature (i.e., 220), followed by °F or °C.
To read boiler settings, press the ‘I’ key to
read the parameter of interest. For example,
press I (HL) High Limit is displayed,
followed by a three-digit number, i.e., 220,
followed by °F or °C. See Figure 24 for
Display Readout Defi nitions.
After approximately 60 seconds without
Text Description Display
Shows
bt Boiler Temperature
HL High Limit
err Error Code
f Degrees Fahrenheit
c Degrees Celsius
Figure 24: Display Readout Defi nitions
any key pressed, the display will enter a
dim display mode. To return to the bright
display mode, simply press any key.
r o r r E
e d o C
n o i t c A / e s u a C
1 r r E . r o s n e s k c e h c ; t l u a f r o s n e S
2 r r E . g n i r i w ™ M O C a r i v n E k c e h c ; t l u a f M O C E
3 r r E . l o r t n o c e c a l p e r ; t l u a f e r a w d r a H
TABLE 5: LED ERROR CODES
d. The operating sequence for L7248C is described
below and shown in Table 6.
The switching action in the L7248C control
has one setting, the high limit, see Figure 25.
The switching relay is controlled by the low
voltage room thermostat. On a call for heat, the
relay contacts make to complete the line voltage
circulator circuit and also the burner circuit if the
boiler water temperature is below the high limit
setting. The high limit switch shuts off the burner
if boiler water temperature exceeds the high limit
setting. The circulator will continue to operate
as long as the thermostat is calling for heat. The
2. Control Operating Characteristics
The L7248C can be in any three (3) operational
states: Normal, High-Limit and Error. The
controller moves back and forth from High-Limit to
Normal state as part of normal operation.
The controller will enter the Error state when there
is an abnormal condition. The operating states are:
a. Normal: Boiler temperature has gone below the
high limit setting (minus the differential) and has
not exceeded the high limit setting.
b. High-Limit: Boiler temperature has gone above
the high limit setting and has not dropped below
the high limit setting (minus the differential).
c. Error: The controller has detected an error
condition (e.g., open sensor) and has shut down
the burner output. The controller continues to
monitor the system and automatically restarts if
the error condition clears. See Table 5.