We have two sinks in an upstairs bathroom. One sink works fine and has no issues with hot or cold water flow. The other sink has cold water but almost no hot water. The hot water flow has been diminishing quickly over the past few weeks. This is the only issue happening in the house. All other faucets and sinks are working fine. What is the suspected cause of losing hot water in one sink? Thank you for your help.
Option A: Some sort of debris (since you indicate a problem of "the last few weeks", not "always been this way") clogging up the section of pipe from where it splits off the pipes that work normally, or (more likely) the valve itself.
If you shut off the supply, unhook the hose to the hot supply, and run it into a bucket, you can see if you appear to have good pressure up to the hose supplying the faucet, or not.
Option B: A "scald prevention" feature in the faucet is malfunctioning.
Option C: you have a child that has discovered playing with valves...