If it were a break underground you would be losing water. It could be that the skimmer is stopped up. Try using a shop vac to reverse blow from the pump basket to the skimmer to clear the line. Do you have 2 valves in front of the pump or more? Should be the one for the skimmer and the other should be the main drain. If you do than can you close the skimmer valve and pull from the main drain with no air in the pump? The other thing you can try is to take a water hose at a slow trickle and put it over the fittings on the ones in front of the pipe one at a time while the pump is running and if the pump fills up and runs normal you have found your leaking fitting or pipe.

Hi muddy,
I haven't tried your suggestions yet. I understand the first one about blowing out through the skimmer, but don't understand the others. I have no valves in front of the pump. (All the valves are on the filter unit.) There are two lines going to the pump, one coming from the pool to the pump/filter, the other going from the filter to the pool. That's it. I can see a drain at the bottom of the pool, but I have no idea what it does, or even if it's connected to anything. The other thing I forgot to mention is that I was getting a few pebbles in the basket, just before the pump, suggesting to me that there is a break somewhere. And.... I haven't noticed any water loss, but it's a large pool, so I may not notice a small leak.
Thanks,
....... john

This post was edited by shakushinnen on Mon, Jun 10, 13 at 12:12

Often a suction leak will draw air and not lose water while running. If you turn the pump off overnight you might notice some water loss.

Sounds like you main drain and skimmer are tied together try blowing out the line from the pump and lets see what happens...

Hi guys,
Alright..... I did as you suggested. I blew air through the line to the skimmer. I got muddy water at first, then clear bubbling, lots of bubbling. I let it run for about a minute, then I hooked up the system as it's supposed to be, and it behaved the same as before (not really getting up to full tilt, just about full tap water from your faucet). This time though, murky water came out of the jets into the pool and the pressure went way up, over 20psi, and I could hear what sounded like pebbles in the lines, like before. So I backwashed it, and rehooked it up to by-pass the skimmer. It sure looks like there's a break somewhere underground.
..... john

Do you live in a freeze area? John try digging up the line in front of the pump until you reach a 90 or elbow and make sure its not there. If not lookup National leak detection in your area and give them a call to locate the broken pipe...

Hope this helps
Rusty

Hi Rusty,
Yes..... I live in Markham, just north of Toronto. The line, just in front of the pump, goes into concrete, and then???
I have two questions .......
1)Does the return line normally go 'under' the pool to the skimmer, or 'around' it. (This pool was probably built 15 years ago, and is quite large.)

2. I've seen posts online to the effect that the skimmer is often a source of an air leak. Could you speak to that?
   Thanks,
   ..... john

The lines from the skimmers and main drains are suction lines, not pressure lines as is the one to the water return jets. As such, they are rarely a point of any measureable water loss when the pump is running
If the water level is too low, you'll hear a sound like a straw in a nearly empty soda, as air is being sucked into the line and pump via the skimmers as water is being drawn out of the skimmer fixture faster than it flows in. A sticking weir, the flap on the skimmer, can also be a cause if it blocks water from flowing into the fixture.
If either the skimmer or main drain lines are broken underground, air will be sucked into the system, and probably dirt, too.
If the lines have been drained for the winter, there will be air pockets in the lines that can take a while to bleed out as the system operates. There will also be some dirty residual water in those winterized lines as it's almost impossible to keep them totally empty and environmental 'stuff' will compost in them over the winter months.

Hi Randy.
When I ran the system, hooked up to the skimmer, there was almost no movement in the skimmer vessel. I ran it for hours that way. I've opened the pool nine times now, and have never seen this kind of behaviour. So...... are you saying that the problem is not likely at the skimmer?
Thanks,
...... john

It's not likely at the skimmer itself.
Your symptoms, dirt and air, are similar to when someone planted a fencepost too close to my skimmer line and cracked the PVC pipe.
If the pipes were not properly drained and winterized, that line may have burst during a hard freeze.

Hi all,
The pool guys just left. They found the leak near the skimmer, but haven't fixed it yet. You may be right Randy, it might have cracked over the winter. I've been closing it for several years, and this is the first problem. When they dig down to it, should the pool guy be able to tell if it was caused by freezing?
Thank you all for your help.
...... john

This post was edited by shakushinnen on Wed, Jun 12, 13 at 19:33

I just fixed my underground leak just below the skimmer. I am almost possible it was caused by a freak desert freeze, but no they wouldn't be able to tell whether it was a freeze or ground shifting, but they may see a tree root growing in it and be able to say that was the cause. Unless you have a special clause for swimming pools your insurance won't cover it no matter what the cause.

The fixing part was super easy it was cutting the 5" concrete deck and digging that was hard.

Hi Crystal,
You were right. They weren't able to tell me the cause of the leak, only that the pipe had a split in it. It's been there a lot of years, so it may have been simple plastic fatigue.
...... john