<span style="font-family: 'Times New Roman'; font-size: medium; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(255, 255, 255); font-family: Arial; font-size: 12px; background-position: initial initial; background-repeat: initial initial; ">Either its goosed itself or forgotten its programming.  In the case of ESCs with a relay for reverse, the symptoms would indicate a relay stuck operated, and either a good thump or  a poke with a pointy thing would set matters right.  In the case of fully electronic ones, one of the output transistors has died or grown a dry joint and won't switch on, so only the pair offering reverse is switching on.  Moderately lucky - the other fail mode is that one of them refuses to switch off, this puts a dead short across power and blows the fuse if there is one, lets the magic smoke out of itself and the wiring if you are less lucky, or incinerates the boat if its a bad day.</div></span>