A flush is only finished when the standing water in the branch has been replaced by fresh water from the main, and the only way to know that has happened is the temperature at the outlet: hot rising to at least 50°C (55°C in healthcare) within one minute, cold dropping below 20°C within two minutes. This timer runs the clock, prompts you for a reading every 15 seconds, detects when the temperature has stopped moving, and logs the whole series with timestamps. You will need a thermometer that reads at the outlet. The tool records and structures your flush — it does not certify that the outlet or the system is safe.
Key points
- Flush little-used outlets weekly, and run each one until the temperature stabilises at target — not for a fixed guessed time.
- Targets: hot 50°C or above within one minute (55°C in healthcare), cold below 20°C within two minutes.
- The timer declares a flush complete when three consecutive readings sit within 0.5°C of each other.
- Open the outlet gently to limit the aerosol, and remove shower spray heads before flushing where you can.
- Copy the finished record into your log book — a flush that is not written down cannot be evidenced.
Open the tap or shower gently at the moment you press Start, then take a temperature reading each time the timer prompts you.
elapsed ·
Flush recorded
Reading series
| # | Elapsed | Temperature | Note |
|---|
Copy this into your log book
Paste it as the note on a “Flushing little-used outlet” entry in the log book, or into your paper log.
This records what was measured, when, and against which target. It is a record of one flush at one outlet — it does not certify that the outlet, or the wider system, is safe or compliant. An outlet that will not reach target needs investigation, not just more flushing.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Why temperature, not the clock
The most common flushing mistake is running every tap for the same guessed number of minutes. That number cannot be right for every outlet: a long branch to a distant room holds far more standing water than a short spur off the riser, so one fixed time either stops before fresh water has arrived or runs on wasting water after it has. Temperature is the honest measure, because the reading only settles at the target once the water standing in the branch has been pushed out and replaced. Hot should reach at least 50°C (55°C in healthcare) and cold should drop below 20°C — when the reading stops moving at the right value, the flush is done. The flushing guide covers the regime behind this, and how long to run taps works through the timing in detail.
How to run a flush with the timer
- Name the outlet as it appears in your written scheme, so the record matches the outlet list an inspector will check against.
- Pick hot or cold, and the setting. Healthcare changes the hot target to 55°C under HTM 04-01.
- Press Start as you open the outlet, gently, to limit the spray. On a shower, remove the spray head first and run a stream where you can.
- Take a reading every time it prompts (about every 15 seconds) with a thermometer held in the flow, and enter it.
- The timer stops you when the reading stabilises — three readings within 0.5°C — or press “End flush & record” yourself at any point.
- Copy the record into your log book with your initials. That entry is the evidence the flush happened.
The targets the timer checks against
| Outlet | Target | What it tells you |
|---|---|---|
| Hot | 50°C or above within 1 minute (55°C in healthcare) | Fresh hot water from the calorifier has reached the outlet and displaced the water standing in the branch. |
| Cold | Below 20°C within 2 minutes | Fresh cold water from the mains or tank has reached the outlet; the branch is no longer holding warmed, stagnant water. |
An outlet that stabilises below target — hot that will not climb, cold that will not drop — is telling you something flushing alone will not fix: a long or oversized branch, a failing TMV, a warming cold pipe, or a calorifier set too low. Record the failed flush, then investigate. The temperature checker explains what out-of-range readings mean, and the temperature chart sets out the full control bands.