[GpsFrontier]

Hello brandonbelew,

Any drain/overflow line needs to have air coming in from above the water line. I attached some examples. Air pockets can form in the overflow line causing all kinds of weird things to happen. If there is a air intake in the overflow line above the water level, it allows the water to flow down freely.

Have you ever stuck a straw in a drink and put your thumb over the top opening, then pulled the straw out of the drink. The liquid stays in the straw, as soon as you take your thumb off the top allowing air in the tube, the liquid flows freely out the bottom. By adding an air intake in the overflow line you accomplish the same effect.

P.S.
So what was the temperature of the water before you added the heater? You never did say, you just said you weren't monitoring it and didn't know.