What water pressure does a thermostatic shower mixer need?

Thermostatic cartridges need pressure to work, and manufacturers state a minimum — commonly 0.5 to 1 bar. Below that figure the valve does not fail safely; it regulates poorly, which is a different and more annoying problem.

Why a minimum exists

A thermostatic cartridge works by sensing the outlet temperature and moving a piston to rebalance hot and cold. It needs enough flow through it to sense anything and enough pressure to move the mix. Starve it and it hunts, overshoots, or simply sits at whatever the supply gives it.

Where this bites

Gravity-fed systems on an upper floor, where the head of water above the outlet is small. A tank in the loft two metres above a first-floor shower delivers roughly 0.2 bar, which is below what most thermostatic bar mixers ask for. Manufacturers publish low-pressure versions for exactly this case.

What to check before buying

The maker’s stated minimum operating pressure, and your own supply. Those are two facts, and the comparison between them is the whole decision. Nothing here replaces the mixer’s own installation instructions or your national plumbing rules.

This does not replace the manufacturer's own instructions. Every dimension, thread size, flow rate, operating pressure, water seal depth and load figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A flow rate is reported with the pressure the manufacturer measured it at, and is never converted to another pressure, because no conversion exists.