In our kitchen sink we have very good flow with the cold water, but barely a trickle with the hot water. We have a low flow aerator and a water filter as well, but if the cold water flows just fine, why would there be a problem with the hot water? We have tried turning the valves and it doesn't make a difference.

Thank you,
Kirsten

Where is your water tank for your hot water located if it is on the same level as your kitchen then gravity won't allow a fast flow I have same problem over in good old scotland not sure if your house are built the same way

Chances are you have some crud right at the faucet. If you have a shut off under the sink, close it. Faucets vary, but this will work with many of them. If not, post back describing yours and the brand and model. Pry the plastic cap off the knob, hot or single knob. Remove the screw under it, and pull the knob off. There should be a nut, or at least something with 2 flats for a wrench. Unscrew it. If you see crud in the cartridge you removed, or under it, clean it out. Maybe hold a towel over the opening and crack the shut off open. Water should flow freely. If so reassemble and the problem should be fixed.

If not, the crud could be at the shut off. Shut the hot water off at the hot water tank. If you shut the inlet off, you must open a hot water faucet to allow for expansion. Disassemble the shut off and clean it, and put back together.