There are a few things to monitor on your pool over the winter season, or when you are not swimming (due to non-winter use). One of these important things to monitor is the pool water level.
If you are noticing that your pool is losing water consistently and it's not from evaporation, you may have a winter pool leak.
If you notice that your winter pool cover is taught and pulling in towards the pool, tearing/ripping or has already slid into the pool, you may have a winter pool leak.
Repairing a vinyl liner in cold climates where freezing occurs is not something that generally can be done successfully. You may be able to locate the leak, but patching can be difficult in near freezing temperatures. In warmer locations, if you can locate the leak you should patch it.
Uncovered Pools (Inground and Aboveground):
For an uncovered pool, start your leak detection by looking for a leak in the liner or plumbing. In warmer locations, you may be able to address a liner leak (if not too cold) by locating the leak and simply patching with a standard vinyl liner patch or patch kit. Note: See checking for a liner leak or testing for a leak below.
Underwater lights, skimmers and vinyl liner step sections are all common areas to check for a leak during winter.
For Aboveground Pools:
In colder locations, if you have an aboveground pool and you suspect you have a leak, monitor your pool for the following concerns.
Is your aboveground solid pool cover is pulling down towards the water or is very taught, or tearing (at grommets, edge seams or even center seams) around the cover? These are signs that would give concern that you may have a winter pool leak. Mesh pool covers will drain water and will not give the same indications unless the water has frozen and is not draining. In this case, you may notice the same concerns as with solid pool covers. Check your pool cover after storms and otherwise occasionally, to spot such problems.
If you have a leak in an aboveground pool that has allowed water to leave the pool under a layer of ice, there is nothing now supporting the ice. You can’t access under the frozen section, the most you can do is to keep adding water to try to support the ice layer. If this ice layer falls, it can rip and tear vinyl liners on it's way down.
The best action to take is to remove the winter cover by releasing the winch and removing the cable from your winter cover. Just simply let the cover fall into the pool. In freezing locations that see snow build up on the covers, you do not want to have a lot of tension on the cover. If you have a leak in your vinyl liner other than trying to add water to fill the void between an ice layer and a water level there is not much you can do to repair a leaking vinyl liner during winter.
The ice level will drop, as will the released cover after the temperature rises. This is the reason to try and maintain a water level under the ice sheet. Damage to your vinyl liner can occur as the ice formation slides down the pool wall. Again, you can try to add water, but if it drains out rather quickly you will need to make the call if you want to continue filling the pool to replace the leaking water.
For Inground Pools:
If you use a solid type of in ground winter cover and have noticed that your pool cover and water tubes are slipping into the pool or are now in the pool, check that your cover pump is not pumping out pool water through a hole in the pool cover. This can be very common, and can give pool owners the false impression that their pool is leaking.
Inground pool leaks can be harder to determine, as underground plumbing is also a factor. If the pool cover seems to be dropping, you can simply remove the water tubes and let the cover drop in the pool. This is the reason that you should use water tubes rather than other objects to weight your lay on the water winter cover. Alternatively, you can fill the pool, beneath the pool cover to replace the leaking pool water.
Finding a leak in your pool during freezing locations is not impossible, but the cold weather makes it less fun. You can simply remove the cover in the pool and deal with it your outside temperature will allow for a repair. Just be sure to not allow the pool water to drop too low; keep half of your water level in the pool at all times.
Fix the Pool Leak:
If you do locate a winter leak in your pool, certainly try to patch it, or make a repair to the leak. More damage to walls, liners or surrounding pool decks can occur by ignoring a winter pool liner leak. If you cannot patch or find a leak in your vinyl pool, due to the winter weather, fill the pool to keep it at least half full - to protect your pool liner and pool walls.
SPP Pool Enthusiast