I'm having some fun and games with a new (to us) pool and its plumbing....
Some context: in ground pool, overflow spa. One main drain, two skimmers - diverter at pad.
We had some work done to replace some of the pool deck, and in doing so some of the pipe work got damaged - primarily the spa & pool returns. I needed to drain the pool below the level of the returns in order to replace the damaged pipe.
So - in trying to drain the pool via the main drain only I noticed the pump losing prime very quickly. Skimmer only is fine - but as soon as the main suction was diverted in the pump would lose prime again. The prime loss is dramatic and instant - barely a trickle of water.
This wasn't previously the case - in the fairly recent past I was able to suction just the main.
I hadn't noticed any water loss - so was assuming an air leak above the water line. I have dug up the obvious candidate locations (joints around the previous damage) but nothing obvious.
So, I reversed the flow - pumping water down the suction line from the pad, hoping that the reverse pressure from the pool would be enough to force water out of the air leak...but nothing.
There is one other location (under the deck at the wall by the main drain) that could be it...but given how much water I pumped back down the line I would expect to see some evidence.
All that, coupled with how vigorously the pump loses prime (I.e. As if here was just an open pipe!) I am wondering if something else is going on.
Is it possible these symptoms could be of a blocked main drain line? That it isn't sucking air in - but essentially creating a vacuum?
The drain has a cover of course - but there has certainly been some debris in the pool during the construction work.
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