As mentioned before I don’t have an 831B receiver but rather an RG731BX which uses the same remote antenna and case as the 831B. When my 731BX receiver is placed in bind mode with the transmitter off, the blue LED does not turn on immediately with application of power to the receiver. It takes more than eleven seconds after power is applied to the receiver before the blue LED starts flashing. This can seem like an eternity if you are expecting it to be on instantaneously.
While the slots are keyed for JR connectors, it is possible to plug in the battery backward. On the horizontal row for the servos - with the receiver label up, the top row of pins is negative, the middle row is positive, and the bottom row of pins are the signals.
Make certain that you have the bind plug in the sensor/bind/power connector slot and not in the AUX3 slot. A defective bind plug could also be the problem. If you are using a home-built bind plug, the two outer contacts should be electrically tied together and the middle contact is left open. If the bind plug is defective or placed in the wrong slot, the blue LED will never flash.
Finally, it is possible you have a defective receiver. Good luck.
Allan