The pool vacuum is a convenient device for keeping the floor of the swimming pool clean. When debris, sunken leaves and bits of dirt or other material collect on the bottom of the pool, it can be all but impossible to remove by hand using other pool cleaning tools like a net. A pool vacuum will suck it up and pull the impurities out of the water by taking them through the filtration system. But if your pool vacuum loses suction, it can't accomplish the task.
The hose that connects the vacuum head to the skimmer basket could lose its prime. This is because the system only works when the hose is filled with water. If air gets into the hose, it will be unable to maintain suction from the pump. Lifting the head of the vacuum above the surface of the water can cause this to happen suddenly. If you are unable to get the vacuum to start at all, it is probably because the hose had air in it to begin with. Before hooking up the vacuum to the skimmer and pump, completely fill the hose with water. Starting at one end you can force the hose underwater, about 6 inches at a time, and then work your way down until the entire hose is submerged and filled. You can also place one end of the hose over the water return near the skimmer and let the jet of water force all the air out of the other end.
Unattached at Basket
Check that your hose is connected at the skimmer basket. This is where the vacuum connects to the suction. The hose usually hooks onto a plate that fits over the skimmer basket and forms a suction seal. If it is not secured tightly, it will not provide the suction you need. If you cannot get it to take hold, you may have a problem with the plate seal. Also, make sure the pump is running normally or there will be no suction to keep the plate attached.
If you have checked the connection and you have primed the hose, but the suction continues to go out, perhaps kicking off the plate at the skimmer connection, you could have a leaky hose. A hose that has holes in it could allow air into the hose and force the vacuum to lose its prime. Even if air is not getting in, a leaky hose could reduce the amount of suction to the vacuum head.
Basket Is Full
The larger debris picked up by your pool vacuum is first filtered at the skimmer, keeping things like leaves from getting into the pump filter. If you vacuum up a considerable amount of large debris, it will eventually fill the skimmer basket and restrict the water flow. This will result in low suction or complete loss of suction. Empty out the basket and you can reattach the hose with better results. You may need to backwash the filter before proceeding as well.