Mixer Tap Temperature Problem: 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

Cartridge fault The mixer may no longer blend or shut off correctly.

Pressure imbalance One supply can overpower the other.

Crossed hot and cold supplies Connections may have been reversed.

Restricted supply side A valve, hose or filter may limit one inlet.

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

Water stays too hot or too cold
Temperature changes when another tap runs
Handle direction seems reversed
One side has weak flow
Thermostatic mixer will not reach set temperature

✓ 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 — Compare hot and cold flow separately Isolate water supplies before dismantling tap components. ⌄

Process

Run each side where the design allows and compare strength and temperature.

Success looks like: A weak or missing side is identified.

Escalate when: The local supply must be restored first.

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

Process

Confirm both supplies are open and not kinked.

Success looks like: Balanced flow returns.

Escalate when: If flow is balanced but temperature is wrong, the cartridge is suspect.

3 Step 3 — Check recent installation changes Isolate water supplies before dismantling tap components. ⌄

Process

Confirm hot and cold connections were not reversed.

Success looks like: A connection error is identified.

Escalate when: Reconnection should be done after isolation.

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

Mixer-tap temperature problems may come from a failed cartridge, unequal hot and cold pressures, crossed supplies, restricted hoses or a thermostatic element that is scaled or misadjusted.

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. ⌄

Descale or replace mixer cartridge.
Balance supply pressures where appropriate.
Correct crossed connections.
Clean inlet filters and check valves.
Calibrate thermostatic cartridge according to manufacturer instructions.

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

Mixer cartridge
Thermostatic cartridge
Check valve
Inlet filter
Flexible tails

! 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.