How long should you run a shower after weeks away?

After weeks away, run the shower until the water reaches full hot temperature — at least 50°C — before anyone uses it, which in most homes means a few minutes of running. Do it with the shower head removed or the flow turned down so the water streams into the drain rather than spraying into the room, because that first flush is precisely when the shower is most likely to be carrying contaminated aerosol.

Why the shower gets its own rule

Every outlet in the house stagnates while you are away, but the shower is the one designed to atomise water into droplets fine enough to reach deep into the lungs — the exact route by which legionella infects. A tap you run for thirty seconds wets your hands; a shower you step into envelopes you in its output for ten minutes. That is why "flush the taps when you get home" is incomplete advice: the shower needs the flush, a controlled method of doing it, and a clean head afterwards. Our page on legionella in shower heads explains the mechanism in detail.

The sequence: flush gently, then clean, then use

The order matters. First, run the water before the spray starts: remove the head where practical, or turn the flow down so it runs as a stream, and let it run to full hot temperature with the room ventilated and nobody standing in the spray. Second, deal with the head itself. Weeks of standing leave scale and biofilm inside the rose that running water does not remove — dismantle it, descale it, and disinfect it following the method in cleaning and disinfecting shower heads. Only then refit and use the shower normally. Skipping the cleaning step is the common error: the flush clears the pipe, but the colonised head re-seeds the water on its way through.

How long is long enough

There is no honest fixed number of minutes, because the correct duration is however long fresh water takes to travel from the source to that shower — short for a combi-fed en suite, longer for a tank-fed bathroom on the far side of the house. Temperature is the measure that tells you the turnover has happened: when the water at the shower is properly hot, the standing water is gone. The same logic applies to the cold side of a mixer, which should run through to below 20°C. Our guide on flushing taps after a holiday covers the whole-house routine the shower flush sits within.

If the shower stands unused routinely

A guest bathroom shower, a shower in a holiday let between bookings, a gym shower in a little-used changing room: anything used less than about once a week is a little-used outlet and should be on a weekly flushing schedule, as set out in flushing infrequently used outlets. Weekly turnover prevents stagnation from establishing in the first place, which is cheaper and safer than a bigger intervention later. Where the shower belongs to a rented property, a holiday let or a workplace, that flush is a control measure, and it only counts if it is written down — date, outlet, temperature reached — in the log book.

What flushing does not fix

Flushing addresses stagnation and nothing else. It will not correct a shower fed by water that never gets hot enough, a mixer whose blended pipe sits permanently in the growth range, or a system with a warm cold feed. If the shower will not reach 50°C, or the cold side stays tepid, the answer is to find the fault — with the help of the temperature checker to document the readings — rather than to flush harder. Flushing is one control within the written scheme, working alongside temperature and cleaning, not a substitute for either.