Thermostatic shower not reaching temperature
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →⚠️ Thermostatic shower valves have a factory-set maximum temperature limit of 38–43°C to prevent scalding. Before assuming a fault, check whether you are simply overriding the maximum stop. Resetting this incorrectly to a higher temperature on a household shared with children or vulnerable adults is a safeguarding risk.
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Most likely cause & what to check
A thermostatic mixer shower maintains a set temperature regardless of pressure changes. If yours is not reaching the desired heat, first check the hot water supply temperature at a nearby basin tap — run it for 60 seconds and feel it. If the basin tap is also lukewarm, the fault is with the boiler or cylinder, not the shower valve.
Most thermostatic valves have a maximum temperature limit cap — a coloured plastic tab or ring under the temperature handle. Remove the handle (usually held by a small grub screw or push-fit cap). The tab can be rotated or repositioned to allow a higher temperature. Consult your valve manufacturer's instructions as the method varies (Grohe, Hansgrohe, Aqualisa, Triton all differ).
If the temperature is uncapped but still insufficient, the thermostatic cartridge inside the valve may be worn or scaled. In hard water areas, cartridges can seize partially open. Isolate the shower valves (quarter-turn service valves on the hot and cold supplies), remove the cartridge (usually a large brass cartridge held by a retaining nut), and soak in descaler for 30 minutes.
If descaling does not resolve it, the cartridge needs replacing. Identify your valve brand and model (often stamped on the cartridge body) and order a replacement — typically £20–£80. Fitting is a DIY job with basic tools if you are comfortable removing the valve handle and cartridge.
If both the cartridge and temperature stop are correct but the shower still runs cool, check the hot and cold supply pressures are balanced — a thermostatic valve requires roughly equal supply pressures to blend correctly. An unvented hot supply with mains cold can cause blending issues.
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