last two weeks the hot water side of the single lever faucet in kitchen has reduced pressure. Rest of the hot water side of faucets in house have normal pressure. Cold water side have normal pressure. on/off valves are turned on normally. where do I look for the problem?
Aerator blockage sometimes happens, but because the cold water pressure (flow) at this faucet is fine, that must not be the problem.
Something could happen to reduce flow through or before the water heater, but because other hot faucets in the house work normally, that must not be the problem either.
All that's left to cause trouble are the valve inside the faucet itself, the hot shutoff valve under the sink, the connector hose, and whatever piping serves only that one faucet.
Decide which of those two valves is easiest to disassemble, do so, inspect for debris, re-install. (The passages inside the faucet valve are probably smaller than those in the shutoff valve and so might get debris lodged in them more easily.) If the problem persists then check the other valve too. If it still persists.. you might be looking at some pipe repair/replacement.