Low Flow From One Tap: Causes, Checks & Fixes

Isolate the hot and cold supplies before dismantling a tap

Use local service valves or the main stopcock. Do not force seized valves or tap handles. Keep water away from sockets and appliances, and stop if a cracked tap body, failed flexi hose or uncontrolled leak is present.

MOST LIKELY CAUSES

Start with these

Blocked aerator Scale and debris collect at the spout outlet.

Isolation valve partly closed The local supply is restricted.

Cartridge blockage Debris can obstruct one side of a mixer.

Kinked or collapsed hose Flexible tails can restrict flow beneath the sink.

◫ Symptom variations Match the exact tap behaviour before repair. ⌄

Only one tap is weak
One side of mixer is weaker
Flow improved after recent plumbing work then dropped
Spout sprays unevenly
Nearby taps have normal pressure

✓ Quick checks Simple checks before removing tap parts. ⌄

Identify whether the fault affects hot, cold or both supplies.
Dry the tap and surrounding area to trace leaks accurately.
Check local isolation valves, flexible tails and visible connections.
Remove and inspect the aerator where flow is poor.
Do not force stiff handles, valves or seized fittings.

If the cause is found: keep the affected supply isolated until the correct repair is completed.

If the leak cannot be controlled: close the main stopcock and call a plumber.

1 Step 1 — Remove and clean the aerator Isolate water supplies before dismantling tap components. ⌄

Process

Unscrew the outlet insert and descale or rinse it.

Success looks like: Flow returns immediately.

Escalate when: If not, the restriction is upstream.

2 Step 2 — Check local isolation valves Isolate water supplies before dismantling tap components. ⌄

Process

Confirm they are fully open without forcing them.

Success looks like: Flow improves.

Escalate when: A seized or damaged valve needs replacement.

3 Step 3 — Inspect flexible hoses Isolate water supplies before dismantling tap components. ⌄

Process

Look for kinks, crushing or sharp bends beneath the sink.

Success looks like: A local restriction is identified.

Escalate when: Internal blockage or cartridge faults need further work.

⌁ Common causes explained Why taps drip, seize, leak or lose flow. ⌄

Low flow from one tap is usually caused by a blocked aerator, partially closed isolation valve, restricted cartridge, kinked flexible hose or debris in the local supply.

Tap faults often come from small internal seals, cartridges, washers and local restrictions. Water can also track down the tap body and appear under the sink away from the true source.

⌘ Advanced diagnostics Plumber-level checks and repair work. ⌄

Flush tap supplies after isolation.
Clean or replace cartridge.
Replace restricted flexible tails.
Check local service valve bore.
Compare static pressure and flow at the connection.

▣ Parts that may need replacing Common components linked to this fault. ⌄

Aerator
Ceramic cartridge
Flexible tap tail
Isolation valve
Tap body component

! When to call a plumber Conditions that should end basic troubleshooting. ⌄

The local isolation valves will not close or are leaking.
A flexible hose is bulging, split or corroded.
The tap body or pipe connection is cracked.
The tap is heavily corroded or inaccessible.
A thermostatic or pressure-balance fault creates a scalding risk.
The leak or poor flow remains after basic service work.

? Frequently asked questions Common questions about tap faults. ⌄

How do I know whether the tap uses a washer or ceramic cartridge?

Traditional screw-down taps usually use washers. Quarter-turn and many lever taps use ceramic cartridges.

Can I replace a cartridge with any similar-looking one?

No. Height, diameter, spline count and inlet layout must match.

Why is only one side of a mixer tap weak?

That side may have a partly closed valve, blocked hose, inlet filter or cartridge passage.