Why Does My Shower Keep Going Hot and Cold?
For a shower that repeatedly changes from comfortably warm to noticeably colder or hotter during use, rather than simply starting at the wrong temperature.
What this usually means
A shower that keeps going hot and cold usually has an unstable hot/cold water balance rather than a single fixed temperature-setting problem. Common causes include another outlet changing the water pressure, a restricted showerhead or hose, a sticking thermostatic cartridge or check valve, an unstable boiler or hot-water supply, or a fault inside an electric shower. The most useful clue is whether the temperature changes only at this shower or at other hot taps as well.
What may be causing this
Water pressure changes when another outlet is used
Clues: The shower changes temperature when someone flushes a toilet, runs a tap, starts a washing machine or uses another shower.
What to do: Test the shower while no other water outlets are running. If the problem disappears, the issue is likely supply pressure, pipe sizing or system capacity rather than the shower control alone.
Showerhead or hose is restricting the flow
Clues: Flow is weak, pulses, improves when the showerhead is removed, or the head has visible limescale.
What to do: Clean the showerhead as the manufacturer recommends and check the hose for kinks or internal collapse. Mira notes that blocked heads or hoses can affect shower performance.
Thermostatic cartridge, filters or check valves are sticking
Clues: The problem affects one mixer or power shower while other hot outlets remain stable, especially on an older or limescale-affected shower.
What to do: External filters that the manufacturer designates for user maintenance may be cleaned as instructed. Internal cartridges, filters and check valves should be serviced or replaced by a competent person.
The boiler or stored hot-water supply is unstable
Clues: Other hot taps also change temperature, the boiler cycles unexpectedly, or hot water runs cool after a period of use.
What to do: Compare the shower with a nearby hot tap. If the hot-water supply itself fluctuates, investigate the boiler, cylinder or system rather than replacing the shower valve first.
An electric shower has a flow or heating fault
Clues: Temperature changes are accompanied by unusual flow changes, fault lights, repeated cut-outs or the issue remains after the head and hose are confirmed clear.
What to do: Follow only the user checks in the shower manual. Do not open an electric shower casing; arrange a manufacturer-approved repair or qualified electrician/shower engineer.
How to check what is happening
Changing demand elsewhere is probably disturbing the hot/cold pressure balance or hot-water capacity.
The fault is more likely in the hot-water source or boiler than in the shower valve alone.
A restricted showerhead or hose is a strong suspect.
The fault is more likely local to that shower's valve, cartridge, pump, filters or internal controls.
Can you fix this yourself?
A homeowner can safely compare other outlets, clean a removable showerhead, check a hose for kinks and follow user-level maintenance in the shower manual. Internal mixer cartridges, fixed wiring, pumps, electric shower components and boiler faults should be left to a competent professional.
- Shower manufacturer manual
- Bucket or shower tray
- Descaling product approved by the showerhead manufacturer
- Torch
What you can safely try
- 1
Identify the shower type before troubleshooting
Work out whether the shower is a mixer, thermostatic mixer, power shower, digital shower or electric shower. The likely causes and safe user checks differ, so use the exact manufacturer manual where possible.
- 2
Test it with no other water being used
Run the shower while nobody uses taps, toilets, washing machines or other showers. If the temperature stabilises, repeat once while another tap is briefly used to confirm whether changing demand is the trigger.
- 3
Check the showerhead and hose for restriction
Clean visible limescale from the showerhead using the manufacturer’s method and inspect the hose for kinks. If the manual allows a head-off test, run the hose safely into the tray or bath and see whether the temperature becomes stable.
- 4
Compare the hot-water supply elsewhere
Run a nearby hot tap and note whether its temperature also fluctuates. If it does, the underlying hot-water source or boiler needs attention rather than treating the shower as an isolated fault.
- 5
Stop at internal components
If the issue remains after the safe external checks, arrange repair of the shower valve, cartridge, filters, pump, electric shower or boiler as appropriate. Do not dismantle electrical shower equipment or remove a boiler casing.
Call a plumber if…
- The shower becomes scalding hot or temperature changes are severe enough to make it unsafe to use.
- Water leaks from the shower unit casing or reaches electrical controls.
- There is a burning smell, buzzing, visible damage, a fault code or repeated breaker/RCD tripping.
- Other hot outlets fluctuate as well, suggesting a boiler or hot-water-system fault.
- Diagnosis would require opening an electric shower, pump, digital processor or boiler casing.
Get the right professional.
This problem can have more than one cause. Start with the checks above: a plumber is the usual first route, while a heating engineer or a electrician may be more appropriate when the clues point that way.
Sources used for this guide
We prefer primary UK guidance, regulators and manufacturers for technical and safety-sensitive claims.
- Why Does My Shower Go Hot and Cold? Causes & SolutionsAqualisa
- My power shower temperature is fluctuatingMira Showers
- Too Hot or Cold: How Seasonal Weather Affects Your ShowerMira Showers
Last reviewed: 31 August 2026. Home Manual updates review dates only when the substance of a guide is checked or changed.