Soaking a shower head in descaler overnight

Does it work?

Disputed

Disputed rather than refuted, because the effectiveness half is settled and the safety half is a genuine disagreement between a chemistry that works and manufacturers who exclude the chemical class from the surface it would be applied to. The catalogue's standing rule applies: where the sources disagree, both positions are recorded and the reader is told which variable would settle it.

This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.

Where not to use it

Why it works

Acetic or citric acid dissolves the calcium carbonate blocking the nozzles by converting it to a soluble calcium salt, and immersion ensures the solution reaches the internal passages that a cloth cannot. Both halves are established. What is not established, and is the actual question, is what the same immersion does over eight hours to a chrome or nickel plating, to a rubber washer, to a plastic insert and to whatever adhesive or gasket sits inside the head. The manufacturers' guidance addresses the finish and does not address immersion, which is why this record stops at conditional rather than either recommending or refuting it.

Background

The acid–carbonate chemistry behind this is sound: limescale is calcium carbonate and an acid converts it into a soluble salt, which is exactly how a commercial descaler works. Where the technique goes wrong is that it treats the fitting as if it were the deposit's container rather than a manufactured object with a finish, seals and often plastic inside it. Two sanitaryware manufacturers in this register exclude harsh, abrasive and acidic cleaners from plated tap finishes and direct that they be cleaned with a mild detergent and dried — and most shower heads are chrome plated over brass or over plastic. The duration is the aggravating factor: a wipe with an acidic cleaner and a rinse is a different exposure from eight hours of continuous immersion, and prolonged acid contact attacks rubber washers and can lift plating at the edges. Two better routes are in the manufacturer's own design. Many modern heads have flexible nozzles specifically so deposits can be rubbed off by hand. And where a soak is warranted, taking the head off and treating only the removable parts keeps acid away from the hose, the seals and the arm.

Conditions

• Applies to plated and plastic shower heads
• The fitting manufacturer's instructions govern
• Duration is the variable that matters most

What it does not do

• It addresses the blockage and not the cause, which is hard water evaporating in and around the nozzles.
• It does nothing for a head whose problem is a perished washer or a blocked hose rather than scale.
• Where the nozzles are silicone, rubbing them clean by hand is what the manufacturer designed for and needs no chemistry.

What to use instead

• Shower head — Blocked by the same carbonate deposit as a kettle, and finished in the one coating that most descaling products are excluded from.
• Descaling — Dissolving mineral deposits with an acid. Effective, well understood, and the wrong answer on any surface made of the same mineral.
• Squeegee — A rubber blade that removes water before it can evaporate. It is the difference between a clean window and a window with the map of its own drying on it.
• Moisture control — The treatment for mould that is not a cleaning product. Every authority in this register puts it first, and it is the only one that stops the problem recurring.