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Splash a small puddle of water onto your workpiece. Jog the torch cap down until it is contacting the water but not the workpiece itself. If the LED is on, your TCHT sensitivity is too high. Decrease the sensitivity 1/16th of a turn at a time until the LED goes out.
If you are having trouble adjusting the ohmic probing system or the LED never comes on, visit Ohmic Probe Does Not Trigger, for troubleshooting tips.