Hot side weak, cold side normal
The cold stream looks full, but switching to hot gives a much smaller stream.
Start here: Go straight to the hot shutoff valve under the sink, then check the aerator for debris.
Bathroom sink water flow problem
Bathroom Sink Hot Water Pressure Low
Direct answer: If your bathroom sink has low pressure on hot only, the trouble is usually local to that sink: a partly closed hot shutoff valve, a clogged aerator, debris in the faucet hot side, or a kinked faucet hose under the vanity.
Most likely: Start under the sink and at the faucet tip before blaming the house plumbing. When cold water is normal and only this sink's hot side is weak, the fix is usually right there at the bathroom sink.
First separate a sink-only problem from a whole-house hot water problem. If other fixtures still have normal hot flow, stay focused on this bathroom sink. Reality check: most of these calls end with a cleaned blockage or a corrected valve position, not a major repair.
Don’t start with: Don't start by replacing the whole bathroom sink faucet. That's a common wrong move when the real problem is a half-open valve or a plugged aerator.
Hot side weak only at this sink?Check the hot shutoff valve and aerator first.
Hot weak everywhere in the house?This page is not the right path; look beyond the bathroom sink.
Last reviewed: 2026-04-05
What low hot water pressure at a bathroom sink usually looks like
Both hot and mixed flow are weak
Hot alone is weak, and the flow stays weak even when you move toward warm or full hot on a single-handle faucet.
Start here: Suspect a restriction on the hot side of the faucet body or a kinked bathroom sink faucet hose.
Pressure dropped suddenly after work or a shutoff
The sink worked fine before a water shutoff, heater work, or supply repair, then the hot side got weak.
Start here: Look for debris lodged in the bathroom sink faucet aerator or hot inlet after the water was turned back on.
Only this bathroom sink is affected
Shower, tub, or another sink still has normal hot flow, but this vanity sink does not.
Start here: Stay local to the sink: hot shutoff valve, bathroom sink supply line, faucet hose, and faucet hot-side passages.
Most likely causes
1. Hot bathroom sink shutoff valve not fully open
This is one of the most common causes when cold is fine and the hot side alone is weak. The handle may have been bumped, left partly closed after a repair, or the stem may not be opening fully.
Quick check: Under the vanity, turn the hot shutoff valve counterclockwise until it stops gently. Compare the hot valve position to the cold valve.
2. Bathroom sink faucet aerator clogged with mineral grit or debris
Debris often gets trapped at the faucet tip after plumbing work or when older valves shed scale. Hot flow can look worse because the hot side carried the debris into the faucet.
Quick check: Unscrew the aerator and run the faucet briefly into the sink. If flow improves sharply, the restriction was at the tip.
3. Kinked or restricted bathroom sink faucet hot hose or supply line
Flexible lines under a vanity can twist, flatten against the cabinet wall, or clog internally. This is especially common after someone stored items under the sink or moved the faucet.
Quick check: Follow the hot line from the shutoff valve to the faucet. Look for a sharp bend, flattening, or a line pulled tight.
4. Debris inside the bathroom sink faucet hot inlet or cartridge passages
If the shutoff valve is open and the aerator is clear, the faucet itself may be catching grit on the hot side. Single-handle faucets often show this as weak warm and hot flow.
Quick check: With the aerator removed, compare hot flow to cold. If hot is still weak right out of the spout, the restriction is farther upstream in the faucet or hot feed.
Step-by-step fix
Step 1: Make sure this is only a bathroom sink problem
You do not want to tear into the vanity if the whole house has a hot water supply issue.
- Turn on hot water at another nearby fixture, like the tub or another sink.
- Compare hot flow there to the bathroom sink in question.
- If other fixtures also have weak hot flow, stop troubleshooting this sink and look for a broader hot water problem.
- If only this sink is weak on hot, keep the diagnosis local to the sink.
Next move: You confirmed the problem is isolated to this bathroom sink, which keeps the repair focused and simple. If hot flow is weak at multiple fixtures, this page is no longer the right path.
What to conclude: A sink-only hot pressure problem usually points to the shutoff valve, supply path, aerator, or faucet on that sink.
Stop if:
- Multiple fixtures have low hot flow
- You see active leaking under the sink when testing
- The shutoff area is corroded enough that touching it may break it
Step 2: Open and inspect the hot shutoff valve under the sink
A partly closed or failing hot shutoff valve is common, easy to check, and often missed.
- Empty enough space under the vanity so you can see the hot shutoff valve clearly.
- Place a towel or small pan under the valve area.
- Turn the hot shutoff valve counterclockwise until it stops gently. Do not force it.
- Compare the hot valve to the cold valve beside it.
- If the handle turns but feels loose, gritty, or does not seem to change flow, note that for later.
Next move: If hot flow returns to normal, the valve was partly closed and no parts are needed right now. If the valve is fully open and hot flow is still weak, move to the faucet tip and hose checks.
What to conclude: A valve that was partly closed is the simplest fix. A valve that feels stripped, seized, or internally blocked may be the real restriction.
Step 3: Remove the bathroom sink faucet aerator and test flow
The aerator is the most common place for grit and scale to collect, especially after water has been shut off and restored.
- Cover the sink drain so small parts do not fall in.
- Unscrew the bathroom sink faucet aerator by hand or with padded pliers if needed.
- Rinse the aerator parts with warm water and pick out visible grit carefully.
- Run the faucet briefly with the aerator off, testing cold first and then hot.
- If the hot stream is now strong, clean the aerator thoroughly and reinstall it.
Next move: If hot flow improves with the aerator removed, the blockage was at the aerator and the repair is done once it is cleaned or replaced. If hot flow is still weak with the aerator off, the restriction is under the sink or inside the faucet.
Step 4: Check the hot bathroom sink supply line and faucet hose for a restriction
A line under the vanity can be visibly kinked, crushed, or clogged, and that is easier to correct than opening the faucet body first.
- Trace the hot path from the hot shutoff valve to the faucet.
- Look for a sharp bend, flattened braided line, twisted faucet hose, or a line pinched against the cabinet.
- Gently reposition stored items or the line itself if something is pressing on it.
- If the line looks damaged, corroded, or permanently kinked, plan to replace that bathroom sink supply line or bathroom sink faucet hose.
- If you are comfortable shutting off water and disconnecting lines, you can briefly crack the line loose at the faucet end into a container to see whether the hot feed from the valve is strong.
Next move: If straightening the line restores flow, keep the line routed with a smooth bend and recheck for leaks. If the line path looks good and hot feed from the valve is strong, the restriction is likely inside the faucet hot side.
Step 5: Decide between a bad hot shutoff valve and a blocked faucet hot side
By now you should know whether the restriction is before the faucet or inside it, which is the point where buying a part finally makes sense.
- If the hot shutoff valve would not open properly, feels stripped, leaks at the stem, or delivers weak flow even with the downstream line disconnected, replace the bathroom sink shutoff valve.
- If the hot supply line or faucet hose is kinked, crushed, or internally restricted, replace that line with the same type and length.
- If hot flow reaching the faucet is strong but flow from the spout stays weak even with the aerator removed, the faucet's hot-side passages are blocked.
- On a two-handle faucet, the hot-side stem or hot inlet area may be the restriction. On a single-handle faucet, the internal mixing cartridge or faucet body passages may be fouled.
- If the faucet is older and service parts are unclear, this is the point to call a plumber or replace the faucet as a separate confirmed project rather than guessing.
A good result: You now have a clear next repair: shutoff valve, supply line or faucet hose, or faucet internal service.
If not: If the diagnosis is still muddy, stop before forcing old fittings and get a plumber involved.
What to conclude: The simple checks have ruled out the usual easy fixes. The remaining problem is a confirmed restriction in the hot shutoff path or inside the faucet itself.
Replacement Parts
Bathroom sink shutoff valve
Bathroom sink supply line
Bathroom sink faucet hose
Bathroom sink faucet aerator
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FAQ
Why is only the hot water pressure low at my bathroom sink?
When only the hot side is weak at one bathroom sink, the cause is usually local: a partly closed hot shutoff valve, a clogged aerator, a kinked hot line, or debris inside the faucet's hot side.
Can a clogged aerator affect hot water more than cold?
Yes. If debris came through the hot side after plumbing work or scale broke loose, the aerator can make the hot stream look much weaker than the cold. That is why removing the aerator is such a good early check.
How do I know if the shutoff valve is bad?
A bad bathroom sink shutoff valve may feel stripped, gritty, seized, or may leak around the stem when you turn it. If flow is weak even when you disconnect the downstream line and test from the valve, the valve is a strong suspect.
Should I replace the whole bathroom sink faucet right away?
Usually no. Whole faucet replacement is often unnecessary when the real problem is a half-open valve, a blocked aerator, or a damaged supply hose. Confirm the restriction first.
What if hot water pressure is low at every fixture in the house?
Then this is not a bathroom-sink-only problem. Look for a broader hot water supply issue, such as a problem at the water heater, a main valve, or debris affecting multiple fixtures.