Why didn't Harry go to Grimmauld Place?

[abbet69 at yahoo.com]

No: HPFGUIDX 89146

Why didn't Harry just go to Grimmauld Place instead of just sticking 
his head in the fire.  He could have checked the house for Sirius and 
if he wasn't in the house, at least he was in London by himself 
without putting his friends in danger.  I don't think there's any 
reason not to believe Harry could use the Floo Network from Umbridge 
office.

Abbet