Thermostatic shower valve — how to service and fix common faults
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Most likely cause & what to check
Thermostatic shower valves have two cartridges: one for temperature (thermostatic) and one for flow/volume. Understanding which one is faulty directs the repair.
If the valve won't reach hot enough temperatures: the thermostat cartridge's maximum temperature limiter may be set too conservatively. Remove the temperature knob and look for a small adjustment screw or a plastic stop — increase the limit slightly.
If the temperature control is stiff: remove the cartridge and clean it with a descaling solution. Limescale on the wax element can make it stiff to turn. Lubricate with silicone grease before reinserting.
If the flow control is stiff or seized: same approach — remove the volume cartridge, clean, and lubricate.
If the valve drips even when fully closed: the cartridge seals have failed. Order a replacement cartridge specific to your valve brand and model (Grohe, Hansgrohe, Mira, Triton all have specific cartridges).
To replace a cartridge: turn off the water supply to the shower, remove the handle and trim plate (usually held by small grub screws accessed with a hex key), then unscrew or pull out the cartridge. Note its orientation before removing.
New cartridges come with fitting instructions and O-rings. Lubricate all O-rings with silicone grease before fitting. Reassemble in reverse order and restore the water supply slowly.
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