Cannot draw out Echtar. Help!

One of my younger brothers is doing his exotic sword quest for a Titan (solar sword). My other brother and I already have our exotic swords. Anyway, he is going to the Founts to kill the warden knights and therefore open the door to go kill Echtar. He gets them all to very low health, pops his Sunbreaker and goes to town with the hammers, one per knight. For some reason though, the door to the Asylum will not open! He's done the same thing three times now. Both my brother and I used Golden Gun and Stormtrance (respectively) for our swords. Any suggestions?