How can I repair my gas heater?

My Rinnai ES38 gives code 99 a blocked vent. The tube to the outside is clear. Is the problem in the burner? Or could it be something else?

Marko2015-01-05T14:31:20Z

Favorite Answer

Recheck the air supply inlet and vent terminal
Page 16

http://www.rinnai.us/documentation/downloads/ES38_1004RFA_Manual.pdf