I had very low pressure coming out of my sink, so i took the aerator off and water flow was normal. Thought it would be simple enough to go buy a new aerator and screw it back on. Got the new one screwed on as tight as i can get it with pliers, and water is coming out of the top of the aerator, and from somewhere water is coming out under my sink as well! Any tips on what to check? the aerator seem to be the right size, it did catch and screw on ok (i think, first time ever doing this).
I think the water is coming from the very top under the sink, so must be something with the aerator, as if i take it off and then turn the water on full blast, no drips under.

its a female aerator.

actually, i tried to put the old one back on, and its doing the same thing. maybe i'm not putting it on right or tight enough? it catches the threads then i get it tight with my hands then use pliers to make it as tight as i can make it.

there should be a thin rubber washer at the top of the aerator. this is what makes the seal.
if you have sufficient number of turns, you can steal the rubber from the old aerator and use 2 washers in the new one.
as for the leak, it is a common problem. the water is running from the top of the aerator and following the spout down to the base and coming thru the mounting hole on the sink. fix the aerator leaks and the leak underneath will go away..

Notice the black washer at the top of the aerator. As packy said, sometimes you have to add a second washer to prevent leaking. You may have been able to take your old aerator apart and clean it. Often little pieces of grit get stuck in the aerator parts inside and stop the water from flowing. There is also a screen in there, looks similar to window screen but has smaller openings. That screen can get mineral deposits stuck in it (sometimes referred to as lime or calcium) if you have hard water, and that will block the water from flowing thru the aerator. You just need to soak it in warm vinegar for a few minutes to dissolve and remove the deposits. This may happen to your new aerator in time, so you can practice on your old aerator to learn how to disassemble and clean it.





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Aerators have threads for attachment. Make sure the threads on the aerator, must match the threads on the spout of the spout. Mis-matched thread will cause water coming out on the top as the aerator is adding resistance to the force of water.

Best Wishes