There are two kinds of Cipher-the simple (or wind) cipher and the relay cipher. In both cases a pipe (or number of pipes) keep sounding even when no keys are pressed.

Wind ciphers are generally caused by sticking or dirty magnet armatures or, more rarely, valve problems. Relay ciphers - which have the same root cause - result in a continuous electric charge to one or more chest magnets thus causing the respective pipes to sound.