Atwood Water Heater

What they said! Check pressure and make sure the soot is cleaned out of the tube. Secondary air is the air that's drawn in with the flame to make it draft. A sooted exchanger will decrease the secondary air flow. There's not much chance of it being wrong but you can check to be sure the orifice is the right size and not damaged. They are usually jeweled and can't be drilled or altered. Make sure the orifice is absolutely clean. That makes a difference with the air/fuel mixing. Webs, dirt or anything else that prevents the orifice from blowing perfectly straight into the burner will decrease the amount of air that gets drawn in with the gas. Craig