Water, water everywhere...

[exnisstech]

FYI: I'm only losing siphon in one of two tubes.

Thats what will happen if the return pump can not provide enough flow for both of them.
The only way they can loose syphon is if the overflow level is low which happens if there is not enough flow from return pump or the water level is too low in the system.
While I'm typing this I had a thought. My u tubes have one side shorter than the other. I wonder if yours are the same and one has the long side inside the tank and the other the short side in the tank? It's only about 1/4" but it would explain why one tube lost syphon and the other did not. I still say you need more flow from the sump but this may explain part of the issue

 

[Dom]

Thats what will happen if the return pump can not provide enough flow for both of them.
The only way they can loose syphon is if the overflow level is low which happens if there is not enough flow from return pump or the water level is too low in the system.
While I'm typing this I had a thought. My u tubes have one side shorter than the other. I wonder if yours are the same and one has the long side inside the tank and the other the short side in the tank? It's only about 1/4" but it would explain why one tube lost syphon and the other did not. I still say you need more flow from the sump but this may explain part of the issue

Yes. It was recently suggested that I drop the overflow deeper into the water as the tubes may be too close to the bottom of the overflow.

I do know that the tubes can be unequal. And I did inspect the tubes and they seemed equal. I'll have to take another look.

I'd really like to get to the bottom of this issue.

 

[Dom]

 

[EeyoreIsMySpiritAnimal]

Float valve with a shut off that your return pump plus into... Same thing you (should) have on your HVAC drip pan

Edit: sorry, I see fish farmer already posted the idea in #20