Our hot water heater throws flames back at us when we try to light it. What could the problem be ?

We can not afford a plumber so i would like to know step by step what i should do. We are both on fixed incomes. Is this problem the thermocouple? Today i replaced the thermocouple and had my brother-in-law come over to light it cause he knows how to well, it still shot flames outward instead of upwards. He thinks the burner may be to rusty. The flames are shooting out instead of up. I vacuumed out the soot that i rubbed off the inside.