Huge Flame on Warm Temperature

Not certified, but I can fix some things here and there. A days ago, my pilot fire went out. Tried to relight, holding down for 60 sec and on pilot, but fire went out as soon as I lifted my finger. No problem, I bought a thermocouple, replaced the old one, and voila fire stays lit. So, I switch the knob to "on" position, and slowly start twisting from "vacation" to "warm". As soon as I hit warm, the fire turns huge and fills up the chamber. Seems way way too large than what it should be. I didn't dare leave it on for more than 5 seconds. Immediately turned off the heater and gas. Any ideas on what's wrong?

 

Welcome to the forums.

The temperature setting just turns the burner on and off. It doesn't control flame size.

While you were changing the thermocouple..... did you vacuum and clean down there ?
Did you have the whole burner assembly out ?

 

I did indeed take out the burner assembly and cleaned the circular disk, though I did not clean the inside chamber of the water heater. I shall try that if and see if it makes any difference.

 

There is a place just before the actual burner where are is allowed to mix with the gas coming out of the orifice. Check that chamber for any unwanted rust and crap. The diagram shows where the orifice is based on that burner. That's the area that needs to be cleaned/vacuumed.