Low pressure on hot side only at one fixture

Quick Answer:

When only the hot side at a single fixture has low pressure while the cold side is fine, the cause is almost always local to that fixture: a partially closed hot shutoff (hot stop), debris in the hot supply line or the heater nipple, or a clogged hot inlet screen or cartridge. Start by verifying the hot stop and flushing the hot feed at the fixture before assuming the water heater or whole-house system needs work.

Why This Happens

Cold and hot water travel through separate paths once the shutoffs and mixing valve are in the fixture. A restriction can be anywhere along the hot path near the fixture: a slightly closed hot stop valve, mineral or solder debris trapped at the heater nipple, a clogged inlet screen or aerator, or debris caught in the faucet cartridge. If only one fixture is affected, the house heater and main hot supply are less likely to be the source.

If the pressure change developed slowly, see Pressure slowly worsening at one fixture. If the hot spray is uneven or sputters, also check Fixture sprays unevenly.

Step-by-Step What to Do

1. Confirm the hot stop (shutoff) at the fixture

• Locate the small shutoff(s) under the sink or behind the fixture for hot and cold. Turn the hot-side valve fully counterclockwise (open) even if it already looks open—valves can be partial.
• Turn the hot faucet on and off to see if pressure improves. If it changes, the shutoff may be partially closed or failing.

2. Flush the hot supply into a bucket

• Remove the aerator or spray head and place a bucket under the spout.
• Open the hot faucet fully and let water run into the bucket for 30–60 seconds. This can push out loose debris from the immediate hot supply and heater nipple.
• Watch the flow and look for particles or sand-like material, which indicates debris in the hot feed that may be clogging the inlet.

3. Check and clean the faucet hot inlet screen (and aerator)

• Many faucets have a small screen or mesh where the hot and cold lines enter the faucet or in the aerator. Unscrew the aerator or remove the inlet screen and inspect.
• Rinse or soak in vinegar to break down mineral deposits, then reinstall and retest.

4. Inspect the cartridge or internal valve parts if the fixture still has low hot pressure

• If flushing and cleaning the screens didn’t help, the faucet cartridge or internal hot-side passages may contain debris. Remove the cartridge per the manufacturer instructions and rinse out any sediment.
• If the cartridge is worn or blocked and cleaning doesn’t restore flow, replace the cartridge. For many single-handle mixers this is a straightforward part swap.

5. If multiple fixtures show low hot pressure, widen the check

• Only if several hot outlets are affected should you look next at the water heater’s outlet, valves, or a whole-house hot-side blockage.
• For a single fixture, focus on the fixture parts and local shutoffs rather than the heater.

What Not to Do

• Don’t drain the water heater for a single-fixture hot-only problem—check the fixture hot inlet first.
• Don’t remove electrical access covers or heater controls unless you are qualified; that’s unnecessary when only one fixture is affected.
• Don’t use chemical descalers in confined fixtures without knowing compatibility with your faucet parts—mechanical cleaning is safer for small blockages.

When to Call a Professional

• If flushing and cleaning the inlet screen and cartridge don’t restore hot pressure.
• If you find continuous grainy debris coming from the hot line (possible heater nipple corrosion or a failing sacrificial anode) or if you can’t access shutoffs safely.
• If the hot stop valve leaks, is seized, or you’re not comfortable disassembling the faucet.

Safety Notes

• Run hot water carefully to avoid scalds when testing. Keep hands and face away from the flow initially.
• Turn off water to the fixture and relieve pressure before loosening fittings or removing cartridges.
• Use basic hand tools and wear gloves and eye protection when cleaning screens or working under sinks.

Common Homeowner Questions

• Why is hot weak but cold is fine? Debris or a partially closed hot-side shutoff or a clogged inlet screen/cartridge usually blocks only the hot path.
• Is the water heater likely the problem? Not if only one fixture is affected; check the fixture’s hot inlet and valve first.
• Can I fix this myself? Often yes — verifying the hot stop, flushing the hot feed, and cleaning the inlet screen or replacing the cartridge usually restores flow.