The Floo Network and the Gryfindor Common Room

[justcarol67]

No: HPFGUIDX 104034

Bren wrote:
Perhaps there are all sorts of charms/old magic protection which 
create a barrier in front of the Gryffindor fireplace.  You can 
see someone's head *in* the fire since it's part of Floo network, 
but once you try to get into the commonroom through fireplace, you 
might not be able to.  After all, we don't see Sirius trying to 
hug Harry in fire or even attempting to make any physical 
fatherly-contact.
 
Beth responded: 
I've noticed, though, that we never see anyone else use the 
fireplaces at Hogwarts. Molly doesn't use it to yell at or visit the 
kids, Dumbledore sends Bill with the message for Arthur instead of of
flooing, etc. I suspect that in general the fireplaces at Hogwarts, or
at least the student area ones, don't work. However, Sirius is aware
of some loophole from his marauder days that lets him slip by. 


Carol notes:
But notice that Snape summons Lupin to his office using Floo powder
and in PoA Umbridge reaches into the Gryffindor fireplace to grab
Sirius by the hair, presumably intending to pull his entire body into
the fireplace in OoP. Also she says that she's closed off (or is
monitoring?) all the fireplaces in Hogwarts except her own, implying
that they are or were connected to the Floo Network. Probably the only
reason Sirius didn't use the Floo Network to enter Hogwarts in PoA is
that he didn't have access to a fireplace. (I don't think the
Shrieking Shack has one and if it does, it's not connected to the Floo
network.)

Carol, who thinks that Umbridge unwittingly did Hogwarts a favor by
exposing a weak point in the defense system (not that I credit her
with good intentions!)