DIY overflor and return

Other possibility...The overflow is taking in air with the water and it's accumulating in the top of the U bend.

 

^ I was thinking more this and if thats the case it could mean there is not enough flow going through it. whats the rating on your return pump?

 

I tracked it down and fixed it. I my overflow pipe I had a barbed fitting attached to a hose that ran to the sump, well the fitting was a 90 degree fitting, it had worked fine for 6 months that it kept losing siphon. Went out an purchased a straight fitting screwed it on and all if perfect now. It was just weird that it worked fine for that long.

 

That is weird glad you got it nailed down

 

Yeah made no sense, I had a straight fitting on the return side and I swapped them around then my return pump could not keep of with the over flow, when I noticed that I ran out and bought a the straight fitting and that was all she wrote.

 

My best guess is the L was slowing the water down enough that the aspirated air was collecting and breaking the siphon