Pump not pulling in water to strainer basket (clogged pipe?). Pump is okay.

I am having an unusual problem. My pump is not filling with water (the strainer basket is empty). This is a 1 HP Whisperflow on 20K in-ground pool. Pool has a suction type cleaner. Here's the background.

1) It started one day about two weeks ago (I noticed a different sound from pump and saw the strainer basket was empty). This happned when the pump was switching from pulling water from Main Drain/Skimmer to pulling from Vacuum Cleaner piping. The pump was running and full of water and when the valve turned to Vacuum, the pump basket emptied and gauge on filter showed 0 (gauge doesn't show vacuum).

2) I could switch the valve back to Main Drain/Skimmer and the basket would fill again and filter gauge would shown about 20 psi.

3) I though the Vacuum Cleaner (which has in-line "leaf" filter) or hose must be clogged. But it was not. If I disconnected the hose from the cleaner port in the pool wall. Pump would then fill with water and run normally (so that was telling me the underground 2" line for Vacuum port was not clogged.) But there was nothing in the Cleaner hose blocking water flow. Very strange.

4) I ran pump without using the Cleaner for a few days. It seemed to work fine so I thought problem must be in Vacuum piping/side. But this weekend the Pump started running dry again. This is with pump pulling from Main Drain and/or Skimmer lines now. I removed top of Jandy valve and can not see any debris in the lines. And how likely is it that both the Skimmer and Main Drain lines would be clogged at the same time?

5) I figured it must be the Pump #1 (maybe impeller is broken). My pool has two 1HP pumps. Pump#1 for the filter/pool-spa/vacuum cleaner, and a Pump #2 is for the Water features. So I swapped pumps. Pump #1 woks fine with the water features - so its not the pump. Pump #1 (now connected to water features) filled up immediately and is pumping fine.

6) I didn't get a change to see what happens with Pump #2 on the "filter/vacuum" setup because I need to go to HD and get some longer 12ga wire to make the connection. But I assume the problem will be there (and that the issue is in the piping or valves some how.

Any ideas on what to check next?

I'll post back once I get Pump #2 reconnected.

Hey CountryBumkin, good to hear from you.

My guess is you have a suction side air leak and you are losing prime. If it happened only when you switched to the vacuum, I would think the leak is within that system BEFORE the pump. As an example, if your vacuum hose floats and has a small leak, when it is not in use it can fill up with air, and then when your pump switches over to vacuum, all that air will cause the pump to loose its prime.

However, since it also happened when you were on the main drain/skimmer, it is likely the pump or any lines the vacuum and main line share, such as the line going into the pump, or the valve. Check the basket lid gasket and valve gasket, if they are worn or old replace them, if not apply some lubricant and replace, see if that helps.

Seconded, especially the pre filter lid gasket seal.

How did it go, CountryBumpkin?