A pool vacuum is a very simple piece of equipment with few mechanical parts. This can make it even more puzzling when it doesn’t work properly. It is an easy piece of equipment to troubleshoot.
Lack of Suction
If everything is connected up and the pump is running, but there is no suction at the vacuum head, there are two possible problems.
The most obvious is that the vacuum hose is not properly connected. You should check that the hose is tightly fitted to the vacuum head. If that is alright then you check that it is correctly fitted at the skimmer or vacuum plate.
If the hose is properly connected then it's possible that it's not properly purged of air. Air in the vacuum tube will prevent the pump from working efficiently. You should be able to hear the extra noise a dry running pump makes.
If none of these is the culprit then the only remaining cause is that the vacuum hose has a leak or is blocked. You will have to lay the hose on the ground. Examine the hose very carefully, because the leak or the blockage will be a significant size if the vacuum did not work at all. You might even spot a leak with water draining through it.
Dirty Water Going Back into the Pool
This is only likely to happen if you by-pass the filters. The likelihood is that you have a sand filter and backwashed it shortly before using the pool vacuum. In all probability, the sand has not had time to settle back into the filter bed, so the filter is not functioning efficiently.
The Vacuum Only Works for a Short While
If the vacuum starts off working well and then stops there are two possible reasons.
The first is that there is a blockage in the vacuum tube that gets washed back when you stop vacuuming. Each time you vacuum, the blockage is taken to the pinch point in the tube. You stop vacuuming and the backflow of water washes the blockage back down the tube. You will have to examine the tube out of the water to see if you can identify the problem area.
The second possibility is that your pool is so dirty that the filter is getting blocked. It could just be that your filters needed changing anyway and the extra load from the vacuum has pushed them over the limit. It could also be that there is some fine contaminant in the pool that is blocking your filters. You will have to have the water tested if that is the case. If your system is set up for it, you can try vacuuming to waste and partially empty the pool in the vacuuming process. If vacuuming to waste has the same problem then you know that it is not the filter that is at fault.