Low Pressure in One Faucet Handle? 4 Real Causes & Fixes

TL;DR: If only the hot or cold side runs weak, the cause is almost always local to that faucet or its supply line, not your whole house's water pressure. Check the aerator first (a 10-minute fix), then the cartridge or valve stem, then the shutoff valve under the sink, in roughly that order.

_Last reviewed: July 2026 · 6 min read_

You turn the handle and the cold water blasts out fine, but the hot side trickles like it's clogged with something. It's not your imagination, and it's rarely the water heater. Nine times out of ten this is a mineral or debris problem sitting right at that one fixture.

Okoniq Property Hub lets you log which fixtures have had aerators cleaned or cartridges replaced, so you're not guessing which faucet was serviced last year.

Why does only the hot (or cold) side lose pressure?

Because hot and cold water travel through separate supply lines with separate shutoff valves, all the way to the point where they mix inside the faucet body. A blockage or restriction on one line has zero effect on the other. This is different from whole-house low pressure, which usually points to the municipal supply, a pressure regulator, or a main shutoff valve that's not fully open.

Hot water lines clog faster than cold lines in most homes because heat accelerates mineral scale buildup, especially in areas with hard water (over 7 grains per gallon is considered hard). If you've lived in the house more than 8-10 years and never replaced a water heater's anode rod, sediment can also break loose from the tank and travel into the hot line, adding to the buildup at the faucet.

Could it just be the aerator?

Yes, and this is the fix that works most often. The aerator is the small mesh screen screwed onto the tip of the faucet spout, and it's the single most common cause of low pressure in one handle only.

Unscrew it counterclockwise with pliers wrapped in a cloth (to avoid scratching the finish), and look inside for a white or greenish crust. That's mineral scale. Soak the aerator in white vinegar for 30 minutes to an hour, scrub with an old toothbrush, rinse, and reinstall. This costs nothing and takes under 15 minutes. If pressure returns to normal, you're done. If it's still weak on that one side, the problem is deeper in the faucet or the line.

Is the cartridge or valve stem the next suspect?

Usually, yes. Modern single-handle faucets use a cartridge that controls both hot and cold flow through internal ports. If mineral deposits build up inside the cartridge on the hot-water port specifically, you'll get a weak hot side even though the cartridge is a single unit. Older two-handle faucets use separate valve stems and washers for each side, and a worn washer or corroded stem on just the hot valve produces the same one-sided symptom.

Replacing a cartridge typically costs $15 to $40 for the part and takes 30-45 minutes if you shut off the water first and take a photo before disassembly (so you remember orientation). Bring the old cartridge to the hardware store to match it exactly. This is a job most owner-operators can do themselves; it's similar in skill level to swapping a ceiling light fixture in terms of tools needed.

| Symptom | Likely Cause | Typical Fix Cost | |---|---|---| | Weak on one side, aerator has crust | Clogged aerator | $0, DIY | | Weak on one side, aerator is clean | Cartridge or valve stem scale | $15-$40 part | | Weak on one side even after cartridge swap | Partially closed shutoff valve | $0, adjust valve | | Weak on one side, sudden onset after other plumbing work | Debris in line from recent repair | Flush line or call plumber |

Could the shutoff valve under the sink be the culprit?

Yes, and this is the fastest thing to rule out before buying parts. Every sink has two shutoff valves under it, one for hot and one for cold, usually oval-handled valves on the supply lines. If someone (a previous owner, a plumber, or you) didn't fully reopen the hot valve after a repair, you'll get exactly this symptom: fine cold pressure, weak hot pressure.

Turn the hot shutoff valve fully counterclockwise to make sure it's completely open. These valves can also corrode partially shut over time, especially in older galvanized or cast iron plumbing systems where internal corrosion narrows the valve opening itself. If the valve looks corroded or won't turn smoothly, that's worth replacing outright rather than forcing it, since a stuck valve can snap.

When should you stop troubleshooting and call a plumber?

Call a plumber if you've cleaned the aerator, replaced the cartridge, and confirmed the shutoff valve is fully open, and the hot side is still weak. At that point the restriction is likely further back in the supply line itself, either sediment from the water heater tank or a narrowing in old galvanized pipe, and that's not a faucet-level fix.

A licensed plumber can run a flow test at the water heater outlet to isolate whether the problem starts there or further downstream. If you're also noticing slow drains elsewhere in the house, it's worth ruling out unrelated issues too. A clogged drain you can sometimes clear yourself, but a hot-water-only pressure drop is a supply-side problem, not a drain problem, so don't confuse the two when describing symptoms to a pro.

FAQ

Why is my hot water pressure low but cold water pressure fine?

This almost always means mineral scale or sediment built up specifically in the hot water line, cartridge, or aerator, since hot water accelerates mineral deposition compared to cold water in the same house.

Can a bad water heater cause low pressure in just one faucet?

Yes, if sediment has broken loose inside an old tank (commonly after 8-10 years without a flush) and traveled to that faucet's aerator or cartridge, though usually this affects multiple hot-water fixtures rather than just one.

How often should I clean faucet aerators to prevent this?

Twice a year is a reasonable schedule in hard water areas, and once a year in soft water areas, taking 10-15 minutes per fixture.

Does low pressure in one handle mean I need a whole new faucet?

Rarely. A $15-$40 cartridge replacement fixes the vast majority of cases; a full faucet replacement is only needed if the faucet body itself is corroded or the cartridge model is discontinued.

Is it safe to use vinegar to clean faucet parts?

Yes, plain white vinegar is safe on standard chrome, nickel, and stainless finishes for soaks under an hour, but avoid prolonged soaking on brass or oil-rubbed bronze finishes since acid can dull the coating over time.

This is educational information, not plumbing advice. Call a licensed plumber if you're unsure about shutting off water lines or disassembling a faucet cartridge.