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Before you decide to strip the covers off of you mattress and search for holes, know that no air mattress holds air indefinitely. You will naturally have to re-inflate your mattress whether or not you have a leak.  Cold air, for example, causes your mattress to shrink. As the house cools down at night, your air mattress will likely soften a bit as the air cools. A space heater by the mattress can prevent this problem. Air mattresses need to “stretch” after they are bought. Don’t be alarmed if they feel soft shortly after you inflate them the first few times, they will quickly adapt. If, after several minutes, it is severely deflated, then you likely have a leak. Sit on the mattress after you blow it up – it should not sink more than 1-2 inches under your weight.  If you are still not sure if there is a leak, leave your mattress inflated overnight and put weight on it, like several textbooks. If it is more than a little deflated in the morning, you have a leak.  Keep the mattress inflated as you search for the leak. If you feel the mattress becoming soft, reinflate it before you start searching again. The higher the air pressure inside the mattress the more forceful the leak will be, making it easier to notice. Hold your hand over the valve and feel for any escaping air. It is usually located right next to the air pump and looks like a plug that you can detach to quickly deflate the mattress. Unfortunately, the valve is the one part of the mattress that is difficult to repair at home. If your valve is broken or leaky, call the manufacturer to order a replacement. The majority of punctures and leaks occur on the bottom of the air mattress after people accidentally leave things underneath the bed. Make sure the bed is fully inflated and then stand the mattress up on its side to examine the bottom. You want enough room to flip, turn, and move around the mattress to easily search for leaks. Slowly move your ear across the entire surface of the mattress, keeping your ear close enough to hear escaping air. When you find the leak, it will sound like a thin, hissing noise, like someone saying “ssssss.” Start on the bottom of the mattress, then try the sides and the front if you don’t find anything. The air escaping from the mattress will quickly evaporate the water, making your hand feel cool. Run your moistened hand along the entire surface of the mattress, 2-3 inches away from it, to search for small leaks. You can also lick your lips and use them to sense escaping air, as your lips are some of most sensitive parts of your body. While some manufacturers warn that this will lead to mold and mildew, soapy water is still one of the best ways to find a leak. It works just like a child blowing bubbles -- you will create a thin layer of bubbly water, and the air mattress will "blow" into it through the leaky hole, exposing in the leak. To do so:  Fill a small bucket with water and a few drops (1 teaspoon) of liquid dishwashing soap. Using a sponge, slowly wipe down the surfaces of the mattress with soapy water. Start near the valve, then check the seams, underside, and top. When you see bubbles forming you’ve found your leak.  Wipe the soap away with a clean sponge when you are done. When the mattress is deflated it will be nearly impossible to find the leak again. Make a note of where the leak is so that you can easily repair it. If you used the soapy water method, use a towel to quickly dry the area near the leak and mark it. Once you’ve found and marked your hole, let all the air out of the mattress. If you used the soapy water method to find the leak, pat the mattress dry with a towel and leave it in the sun for at least 1-2 hours before returning to it.
Know that all air mattresses lose air naturally. Inflate the air mattress fully to test for a leak. Check the valve holding in the air. Stand the mattress up on its side in a quiet, large room to examine it for leaks. Place your ear 2-3 inches away from the mattress and listen for hissing sounds. Wet the back of your hand and repeat this process if you can’t find anything. Use soapy water to search for bubbles if you still cannot find the leak. Circle the leak with a pen or sharpie. Deflate and dry the mattress completely.