My 100P series SCR Power control is not working properly. It will not shut off the output fully.

Below are some troubleshooting steps that can help to determine the problem. 

1) Make sure that you have a load (heater) connected to the output and that any output fuses are not blown.  You cannot check operation without a suitable load connected.
2) Check that the output range on the control matches the output range of the SCR power control. Disconnect the output signal from the temperature control and check whether you still have output to heater.  If the output goes to zero then there could be a problem with the temperature control.  Check the output range of the controller with a suitable meter.
3) Disconnect the 24VAC and the line voltage from the SCR controller. Disconnect the signal from the temperature controller to the SCR controller.  Measure the resistance across the signal input terminals of the SCR power controller.  The resistance is typically set to 500 ohm for 4-20ma outputs. 
4) Check the output range of the controller with a suitable meter.  For 4-20mA controls you should connect a multimeter set for 20+ milliamps in series with one of the signal leads to the SCR power control.  Confirm that the control signal is as required.  You should be able to adjust the control output by using auto /manual on the control (if provided) or changing the temperature setpoint significantly above and below the process temperature as displayed on the temperature controller.
5) Remove Power from SCR controller, disconnect the heater and measure the resistance across the output (Line & Load) terminals with an analog tester like a Simpson 260 on the RX100 range.  Resistance should be infinite.
6) Try adjusting the bias and gain settings on the SCR power control.