---
title: "Temperature profiling your water system: going beyond sentinel checks"
source_url: https://legionella.io/articles/temperature-profiling-your-water-system-going-beyond-sentinel-checks/
canonical_url: https://legionella.io/articles/temperature-profiling-your-water-system-going-beyond-sentinel-checks/
pillar: "Monitoring, Flushing & Sampling"
summary: "Sentinel checks watch two outlets; temperature profiling rolls through the rest. What profiling is, how to plan it and how often, so no branch is left unseen."
primary_keyword: "temperature profiling water system"
date_published: 2026-06-27
date_reviewed: 2026-06-27
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Quote, adapt or republish with attribution to REMOTE TECH LTD and a link to source_url."
license_url: https://creativecommons.org/licenses/by/4.0/
---

# Temperature profiling your water system: going beyond sentinel checks

Monthly sentinel temperatures are a fixed part of most monitoring schemes, and they earn their place. The trouble is what they do not see. A sentinel check looks at the outlet nearest to and furthest from each calorifier or storage point, on the reasoning that if the two extremes of a circuit are in range, the parts between them probably are too [1]. That assumption holds on a simple, well-balanced system. It does not hold on a building full of dead legs, oversized branches, intermittently used outlets and odd pipe runs that have grown by accretion over decades. Between your two sentinels there can be a tepid branch sitting at the wrong temperature for months, never sampled, never flagged.

Temperature profiling is the discrete task that closes that gap. This article assumes you already run sentinel rounds and want to set up the wider survey that confirms control everywhere.

## What temperature profiling is

Profiling is a periodic, rolling survey of a representative set of all outlets, spread across a defined period so that every outlet is checked at least once within that window. HSG274 Part 2 describes representative (rolling) temperature monitoring of a proportion of outlets carried out in addition to the monthly sentinel checks [1]. Where sentinels are the same two outlets each month, profiling moves around the building over time, working through the outlets that sentinels skip.

The point is coverage over time rather than coverage every month. You are not trying to read every tap in one visit. You are setting a rotation so that, across the defined period set by your risk assessment, no outlet stays permanently unseen. The reading you take is the same kind of reading as a sentinel temperature, hot water at the outlet and cold water at the outlet, taken after a defined run time. The difference is which outlets you visit and how you schedule them.

## Why sentinels alone are not enough

Sentinels prove the extremes of a circuit. They are excellent at catching whole-system failures: a calorifier running cool, a cold tank warming up, a circulation pump that has stopped. What they cannot catch is a localised problem on a branch they do not touch.

Consider a guest room rarely let, a cleaner's sink in a back corridor, a shower in a plant area, or a long-throw run to a single basin. Each of these can sit outside the sentinel path. If the branch is poorly insulated, oversized for its flow, or barely used, its water can drift towards the range that favours Legionella growth without any sentinel ever showing it [3]. Profiling is how you find those outlets before a sample does.

## Implementation sequence

The following sequence sets up profiling from an existing sentinel scheme. Treat the frequencies and proportions as risk-assessment-led; the numbers below are illustrative, not prescriptive [2].

1. **Build or confirm the asset and outlet register.** List every outlet served by the system, with a unique reference, location, type (tap, shower, spray, etc.), and the circuit or zone it sits on. Profiling is only as complete as the register behind it. If outlets are missing from the list, they are missing from the survey.

2. **Group outlets by circuit and by risk.** Cluster each outlet under its hot and cold circuit, then rank by risk: aerosol-generating outlets, infrequently used outlets, vulnerable-occupant areas and known awkward runs sit higher. This grouping decides who gets visited more often within the rotation.

3. **Set the rotation so every outlet is covered over the defined period.** Decide the period over which the whole population is profiled, commonly an annual cycle, and divide the outlet list across your monitoring visits so the coverage completes within it [3]. Higher-risk outlets can appear more than once per period; low-risk, well-controlled outlets may appear once. The risk assessment sets both the period and the proportion sampled each round [2].

4. **Define and record the reading method.** Fix the run time before you read (for example, the time to reach a stable temperature), state where the reading is taken (at the outlet), and record the instrument used and its calibration status. Consistency matters: a profiling reading is only comparable month to month if it is taken the same way each time.

5. **Take readings and log them against the outlet reference.** Record hot and cold temperatures, the date, the operative, and the run time. Tie each reading to the register reference so trends can be followed for an individual outlet, not just the building as a whole.

6. **Flag and investigate out-of-range outlets.** Any outlet outside the expected range is an action, not a number to file. Re-check, look for the cause (dead leg, missing insulation, blending upstream, low use), and apply a remedy such as flushing, insulation, removal of the redundant pipework, or repair.

7. **Feed findings back into the scheme.** Use the results to revise the monitoring frequency, promote a recurring offender to more frequent checks, or escalate to the risk assessment for review. Profiling that does not change anything is just data collection.

## Sentinel versus profiling at a glance

| Feature | Sentinel monitoring | Temperature profiling |
|---|---|---|
| Outlets covered | Nearest and furthest on each circuit | Representative set, rotating across all outlets |
| Frequency | Typically monthly | Rolling across a defined period, risk-assessment-led |
| Purpose | Detect whole-circuit failure | Confirm control everywhere, catch local cold or tepid branches |
| Same outlets each time? | Yes, fixed | No, rotates over the period |
| Set by | Scheme and guidance | Risk assessment (period and proportion) |

For the foundations these two tasks share, see [sentinel outlets: what they are and how to monitor them](https://legionella.io/articles/sentinel-outlets-what-they-are-and-how-to-monitor-them/) and the practical round in [the sentinel temperature monitoring round: a field SOP](https://legionella.io/articles/sentinel-temperature-monitoring-round-field-sop/). Where profiling repeatedly finds outlets that cannot hold temperature, a remediation step such as [thermal disinfection using heat to control Legionella](https://legionella.io/articles/thermal-disinfection-using-heat-to-control-legionella/) may form part of the response, alongside design fixes.

## Common pitfalls

The most common failure is an incomplete register: outlets added during refurbishments never make it onto the list, so they are never profiled. The second is treating profiling as an audit you do once rather than a rolling commitment. The third is recording readings without acting on them. Profiling generates value only when the out-of-range outlets feed back into flushing schedules, insulation works and the risk assessment review.

## Frequently asked questions

### Is temperature profiling the same as sentinel monitoring?

No. Sentinel monitoring checks the same fixed outlets, typically the nearest and furthest on each circuit, usually each month. Profiling is a rolling survey that rotates through a representative proportion of all outlets over a defined period so the whole system is covered in time [1]. They complement each other and are normally run together rather than one replacing the other.

### How often should I profile the whole system?

The frequency and the period over which full coverage is achieved are set by your risk assessment rather than by a single fixed rule [2]. A commonly used arrangement is to complete coverage of all outlets across an annual cycle while continuing monthly sentinels, but a higher-risk building may justify a shorter cycle. Document the rationale and review it whenever the system or its use changes.

### How many outlets need profiling?

The proportion of outlets profiled in each round, and over the full period, is determined by the risk assessment, not by a universal percentage [2]. The aim is that all outlets are checked over the defined period [3], with higher-risk outlets visited more frequently within it. Record the chosen proportion and the reasoning so it can be justified and reviewed.

### What do I do with an out-of-range outlet found during profiling?

Treat it as an action. Re-check the reading, then investigate the cause, which is often a dead leg, missing insulation, low usage or upstream blending. Apply the appropriate remedy, such as flushing, insulation, pipework removal or repair, and feed the finding back into the monitoring scheme and, where needed, the risk assessment.

## Sources

[1] HSE, HSG274 Part 2 (2024), The control of legionella bacteria in hot and cold water systems, Operation and inspection of hot and cold water systems, p.70. https://www.hse.gov.uk/pubns/books/hsg274.htm

[2] HSE, HSG274 Part 2, The control of legionella bacteria in hot and cold water systems (frequency and proportion of outlets set by the risk assessment). https://www.hse.gov.uk/pubns/books/hsg274.htm

[3] HSE, HSG274 Part 2, hot and cold water guidance (all outlets checked over a defined period). https://www.hse.gov.uk/pubns/books/hsg274.htm