I have a cheap brand 4 ch remote and 6ch receiver for one of rc planes. The receivers ch3 doesn't pick up a signal but gives a little jerk when the servo is plugged in. The brushless motor will not run on this channel but will run on others. Likewise a servo will not run on it but will only twitch slightly when connected. I think its my reciever that is the problem. But could it also be my throttle input on my remote? Like could it be the throw isnt working? Or will the rudder throw not work too then?

It could be the receivers throttle channel or the throttle potentiometer (a type of sensor) in the transmitter. Do you have a known-good receiver to try with the transmitter?

yep could be either the Transmitter or the receiver...you'll need to find another receiver on your channel to check your transmitter.....(by the way....the term remote isn't used much)
Good Flyin