Here's the setup: Bathroom sink faucet with two handles. All working great to start.
I had to shut off the hot water valve for a moment. I did that. When I turned it back on, the hot water came back on, but at about 50% of the previous flow. That's weird. Not sure what happened, and thought maybe the valve closure kicked loose something that got caught in the aerator. But cold water pressure was perfect going through the same aerator. (Checked the aerator anyway, and it was fine.)
Then I thought maybe the way I had turned the hot water back on had messed something up - maybe with the way the hot and cold joined together. So I tried turning the hot valve off/on with the hot water faucet opened up full. Now hot water is barely present: a trickle -- maybe 5% of original flow. Tried going off/on with the cold water flow opened up full. Same result. Cold water is 100%. Hot water is 5%.
Where should I look next? The hot water heater is fine (flow to all other sinks and showers is fine). It's definitely at the faucet level.
Air in the line? (I don't know how to figure that out or what to do).
The cartridge inside the hot water handle? And what would I do there? I've seen references to backflushing the faucet, but I'm not sure how to do that. But I'm game to learn.
Thanks in advance for the help.