Direct answer: If one faucet will not get hot water but other fixtures do, the trouble is usually right at that faucet: a closed hot shutoff, a kinked or clogged hot supply line, or a faucet cartridge that is not opening the hot side. If no fixture gets hot water, stop at the faucet and check the water heater side instead.
Most likely: On a single-faucet complaint, the most common causes are a partly closed hot stop under the sink or a worn faucet cartridge.
First separate a faucet-only problem from a house-wide hot water problem. That one decision saves a lot of wasted time. Reality check: a bad faucet cartridge is common, but a bumped shutoff valve under the sink is even more common. Common wrong move: buying a new faucet before checking whether the hot stop is actually open and feeding the faucet.
Don’t start with: Do not start by replacing the whole faucet or the water heater just because the water stays cold at one sink.
Other sinks, showers, or tubs still get properly hot water, but this faucet stays cold or barely warm.
Start here: Start under that sink or vanity. Check the hot shutoff position and the hot supply line before blaming the faucet body.
Cold water runs normally, but when you move to hot, flow drops off hard or trickles.
Start here: Look for a closed stop, a kinked faucet supply hose, or debris blocking the hot side of the faucet cartridge.
The handle moves normally, but the water only gets mildly warm even after running it.
Start here: Confirm other fixtures get hotter water first. If they do, suspect the faucet cartridge or a hot-limit setting on that faucet if it has one.
Kitchen, bath, and shower all stay cold or lukewarm.
Start here: Do not tear into this faucet yet. The problem is likely upstream at the water heater or the main hot-water supply.
This is common after cleaning, cabinet work, or someone bumping the valve. It can leave you with weak hot flow or no hot flow at one faucet while the rest of the house works normally.
Quick check: Look under the sink and make sure the hot stop is fully open. On most valves, the hot side is on the left supply line.
A braided faucet line can get twisted during storage or previous repairs, and debris can lodge where the line or faucet connects. That usually affects one faucet only.
Quick check: Follow the hot line from the shutoff to the faucet. Look for a sharp bend, flattening, or a line that feels twisted tight.
On single-handle faucets especially, the cartridge meters both hot and cold. When the hot side sticks or plugs up, the faucet may stay cold or only go lukewarm even with normal cold flow.
Quick check: If the hot stop is open and the hot line looks fine, but only this faucet will not get hot, the cartridge moves to the top of the list.
If several fixtures are cold, or hot water fades everywhere, the faucet is just where you noticed it first.
Quick check: Run hot water at another sink or tub. If that fixture also stays cold, stop diagnosing the faucet and move upstream.
You do not want to pull apart a faucet when the real problem is the water heater or the house hot-water supply.
Next move: If other fixtures get hot normally, you have narrowed this down to the faucet or its local hot supply. If other fixtures also stay cold, this page is no longer the right repair path.
What to conclude: A single-faucet failure points to the shutoff, supply line, or faucet internals. A whole-house failure points upstream.
A partly closed stop is the fastest, safest fix and it causes a lot of one-faucet hot-water complaints.
Next move: If hot water returns or hot-side flow improves right away, the shutoff was the problem. If the valve is already open and the faucet still stays cold, move to the supply line and faucet checks.
What to conclude: An open, dry shutoff rules out the simplest local cause. A leaking or seized shutoff is a separate repair, but it is not a faucet part.
A damaged or plugged hot line can starve the faucet even when the shutoff is open.
Next move: If you find and correct a simple kink and hot flow returns, you have your fix. If the line looks normal and the problem is still only at this faucet, the faucet cartridge becomes the leading suspect.
Mineral grit or debris can lodge in the faucet and mimic a failed cartridge, especially after plumbing work or a shutoff being turned off and on.
Next move: If removing debris or correcting the hot-limit setting restores normal temperature, you can reassemble and verify operation. If hot flow remains weak or the faucet still will not get hot, the cartridge is the most likely repair part.
Once the hot stop is open, the hot line is not kinked, and the outlet is not the restriction, the cartridge is the part most likely blocking or mis-metering the hot side.
A good result: If the faucet now reaches normal hot temperature and the handle mixes smoothly, the cartridge was the fault.
If not: If a new cartridge does not restore hot water, stop buying faucet parts and look for a hidden supply-side blockage, a cross-connection issue elsewhere, or a faucet-specific defect that may justify full faucet replacement.
What to conclude: A successful cartridge replacement confirms the failure was inside the faucet. No change after replacement means the problem is likely upstream of the cartridge or the faucet body itself.
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When the rest of the house still gets hot water, the problem is usually local to that faucet. The usual suspects are a partly closed hot shutoff, a kinked or clogged hot supply hose, or a faucet cartridge that is not opening the hot side.
Yes. On many faucets, especially single-handle models, the cartridge controls both hot and cold mixing. If the hot side of the cartridge sticks or plugs with debris, the faucet may stay cold or only get lukewarm.
That usually points to a restriction on the hot side, not a general faucet problem. Start with the hot shutoff valve, then the faucet hot supply hose, then the cartridge.
Not first. Whole faucet replacement is often unnecessary on this symptom. Check the hot stop, the local hot supply line, and the faucet cartridge before you spend money on a full faucet swap.
Usually not by itself. A clogged faucet aerator more often reduces overall flow. But removing it is still a smart check, because debris at the outlet can hide a deeper hot-side restriction and it is easy to rule out.
Then this is probably not a faucet repair. Look at the water heater, recirculation setup if you have one, or the main hot-water supply path instead of taking apart the sink faucet.