Change the battery.
Recode handset (refer below).
Check for obstruction or interference to frequency.
If Stanley handset, check to ensure that dill switches match up with the receiver.
Check that the unit is engaged on automatic operation.
Ensure that power is turned on.

With the power turned onto the unit press and release the small button (learn button) and the yellow LED will come on indicating that your unit is ready to accept code.
Press the handset button once. If the code is accepted the green LED will blink twice.
For multiple handsets code them in at this stage.
Press and release the small button (learning button) and the yellow LED will go off.

Check manual operation for correct balance, not binding. Adjust if necessary.
Spray silicone lubricant into tracks. Do not grease.
Check/adjust safety sensitivity setting.
Check limits.

At Control Box.
Check power is on to Control Unit (Red LED illuminated).
IF NOT, check mains plug and fuse.
Plug fully engage on top of Control Box.
Motor wiring connections properly engaged.
Manual release lever in “engaged” position.
Limit switch cams correctly set, i.e. upper Limit Switch for fully open position, lower Limit Switch for fully closed position.
move door manually to half-closed position and try again.
Try operation with Hand Transmitter

Check bottom limit switch setting.
Adjust if necessary.
Call service technician.

To disengage – Pull manual release lever (red handle) downwards.
To engage – Push manual release lever up.

Spring tension may require adjustment.
Call service technician.