Diagnosing pump leaks

• 1). Use the magic marker to make a small line along the top of the pool's waterline. This will be the guide by which you can tell whether or not your pool pump still has a leak.
  
  
• 2). Inspect the pool pump assembly while it's running for any obvious signs of water running from its seals. The most common and visible source of a leak is in the pool filter due to the fact that the screw-on top of the filter canister often develops a build up of sediment or detritus along the interior rim. Water will leak from the joint between the top and bottom of the canister.
  
  
• 3). Turn off the pool pump, unscrew the top of the filter canister, clean and scrub both the top and bottom threads of the canister, then smear the threads with glycerin gel before reassembling the filter canister. This will form a water-proof protective layer that will stop the canister from leaking. Should the pool's water level still be dropping steadily over the next few days, the source of the leak has not been found.
  
  
• 4). Disconnect the filter/skimmer/run off valve from the intake of the pool pump. This device is made of either PVC pipe or painted aluminum, both looking like a 4-way junction. Some pump models require a socket set to remove the bolts and some take a rubber strap wrench to unscrew the protective sleeve covering the joints between the pipes coming from the pool's intakes and the pool pump.
  
  
• 5). Turn the handle on the top of the disconnected valve to the skimmer setting and use the garden hose to add water to the main drain intake of the valve. Since the valve is set to only allow water from the pool's skimmer pipe to pass through, the valve should block off any water you pour into the main drain intake. If the valve is defective, it will allow water to pass out the drain port. Normally, the drain port is only activated when the water pressure within the intakes exceeds a given upper limit. In this case, the entire valve assembly isn't working properly and so it is sending water from the pool to a drain waste pipe. The valve assembly is the source of the leak and must be replaced.
  
  
• 6). Shut off the flow of water from the skimmer while the pool pump is running. This can be done by manipulating the valve assembly which you've assured is working correctly. With no negative pressure from the pump, no water will pass through the underground skimmer pipeline. If the pool's waterline still continues to drop, then the leak is in the underground main drain pipeline. Over time, these lines can become either cracked or loose along the pipe joints. This is a costly problem which can only be repaired by a professional because the repair requires the entire pipeline be dug up.
  
  
• 7). Change the flow of water from the main drain to the skimmer, which you've now assured is functioning properly. This will definitively stop the pool pump's loss of water and prove that the leak is in the main drain pipeline, which, again, is a costly issue to repair.