Mixer shower running too hot — cannot get cold water
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →⚠️ Scalding hot water from showers is a safety hazard, especially for children and elderly users. Do not use the shower until the temperature is controlled.
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Most likely cause & what to check
Check both supplies — confirm cold water is reaching the shower valve by briefly opening the cold isolation valve on its own. If no cold water is present (e.g. the cold feed tank is empty or the isolator is closed), the shower will run on hot only.
On a thermostatic mixer shower, the thermostatic cartridge controls temperature. A failed cartridge can cause the valve to default to hot. The cartridge can be replaced without replumbing — costs £20–£100 depending on the brand.
Check the anti-scald stop on the temperature handle — most thermostatic showers have a factory-set maximum temperature limiter. This is usually a small tab or screw under the temperature handle that limits rotation. Ensure it has not been removed or damaged.
Some shower thermostatic cartridges have a maximum temperature adjustment screw on the cartridge body — consult the shower manufacturer's installation guide.
If the cartridge is more than 8 years old, particularly in a hard water area, replacement is the most reliable fix. Brands such as Mira, Triton, Bristan, and Grohe all have spare cartridges available.
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