The G29 command is just the probing command, you need to send the M280 command to extend the probe, then G29 and then the M280 command again to retract the probe. Sorry I don't have a BL touch so cannot advise on the actual gcode but my sequence for auto probing the bed with a servo operated optical sensor is
G28
M280 P0 S5
G29
M280 P0 S85
G1 F8000 X0 Y0 Z150
Its not an issue with your firmware, these settings are in the script folder of your controller software (pronterface/cura/mattercontrol/whatever) Which one are you using?