How do I know when a steam machine needs descaling?

When it takes noticeably longer to reach pressure, produces wetter steam, or spits water — and by then you have left it later than you should.

There is no moment of failure. Scale builds on the heating element, heat transfer worsens, and the machine gets slowly worse over months. Most owners conclude the machine was never very good.

Work to the schedule in the manual rather than to symptoms, and halve the interval if you are in a hard-water area. Your supplier publishes the hardness for your postcode.

Machines that take a descaling cartridge treat the water going in, which is a better arrangement than periodic descaling — but price the cartridges before you commit to the brand.