All drain back systems start with no water in the manifold until it turns on and cold water is pushed into the hot manifold.

I hadn’t considered this before, but yesterday I hooked it all up and tubes were so hot my thermocouple threw an error since it only goes up to 230F degrees. I looked online and folks were seeing 320 degrees prior to running water through the manifold.

So then I removed the probe from the copper tube and placed it 1/2 inch from the manifold tube (further away so I could get a digital readout) and saw 200 degrees.

Not having any other ideas, I pushed cold water today and there wasn’t an explosion 🙂 . . . so on the one hand my experience and the fact that all drain back systems start the day water-less suggests a hot start is OK. On the other hand, I find it hard to believe you can suddenly introduce cold water into a relatively small copper pipe that’s over 300 degrees and not have some sort of failure.

Thoughts?