Boiling sound from nearside Plenum ???

Ok was having a bit a fun with a WRX the other day car got mega hot and the rad hoses where solid with a water boiling noise from the drivers side under the plenum. Now I've heard of problems with the small pipes under there blocking and causing poor water flow, I've also read that the plenum warming pipes can be by passed with one pipe. Has anyone else had this and can the bypass be done with the plenum in place????

Thanks in advance

Craig

P.s everything else has been checked there's no air in the system and my heater matrix has also been bypassed.