MODERN BURNER UNIT (MBU)
UNIT MAINTENANCE PROCEDURES
Replace Feedback Potentiometer. To replace the feedback potentiometer assembly (1), remove the
Control Knob (2) as described earlier . Remove the two screws (3) with a crosstip screwdriver. Disconnect
the feedback potentiometer wiring harness (4) by separating the connector at the end of the harness.
Remove the feedback potentiometer assembly.
Install a new feedback potentiometer assembly (1) on the fuel delivery block (5). Secure the two screws
(3) with a crosstip screwdriver. Reconnect the feedback potentiometer wiring harness assembly
connector (4). Install Control Knob (2) as described earlier.
The calibration procedure outlined below in NOT REQUIRED if the Controller Assembly
software version is 2.0 or higher. The software version is displayed on the liquid crystal
display on the lower right front corner of the Controller Assembly on power up.
To check the software version, be certain that the MBU is powered down, the press the power
button on the front of the MBU. After the normal power-up display sequence, the software
version will be displayed if the version is 2.0 or higher. If the software version is NOT
displayed on power-up, the calibration procedure detailed below MUST be performed.
If the Calibration function is selected in error (by pressing and holding the Power button
longer than 3 seconds), either wait 10 seconds or press the STOP button to return to standby
After replacing the Feedback Potentiometer perform a calibration procedure by first making sure that the
MBU is powered down and cool.
Press and HOLD the Power button until the power-up routine is complete (approximately 3 seconds) and
the hour meter displays CAL?
Release the Power button.
Press the Start key. The hour meter will display CAL.
Turn the Burner Control Valve through its complete rotation from HIGH (Start) to LOW.
Wait approximately 3 seconds for automatic return to standby.
MBU is ready to use.