Short answer: a monthly Legionella temperature log records each sentinel outlet's temperature, how long the water ran, whether it met the target and what was done. HSE's HSG274 Part 2, Table 2.1, sets the targets: calorifier flow at least 60 °C, return at least 50 °C, hot outlets at least 50 °C within one minute, cold outlets below 20 °C within two minutes.
Download the log as a CSV file for Excel, Google Sheets or Numbers. No sign-up needed.
What the log covers
The monthly readings are taken at sentinel points, chosen to represent the whole system. In a simple cold water system they are "typically the furthest tap (far sentinel) and the nearest (near sentinel) to the supply or storage tank" (HSG274 Part 2, para 2.59). In a hot system without circulation they are the taps nearest and furthest from the calorifier, plus the ends of significant spurs (para 2.62). In a circulating system the far sentinels are the return legs towards the end of each loop (para 2.63). HSE says each time that the layout of the pipework matters more than where the outlet happens to be.
Subordinate loops are smaller loops branching off a principal loop. They are read so that every one is covered each quarter, which Table 2.1 suggests doing "ideally on a rolling monthly rota" (para 2.64 and Table 2.1). The log template has a row for that.
Targets for each reading
| Reading | Target | How often |
|---|---|---|
| Calorifier flow | As close to 60 °C as practicable, not below 60 °C | Monthly |
| Calorifier return | Not below 50 °C | Monthly |
| Principal loop return legs | At least 50 °C (55 °C in healthcare premises); surface readings on metal pipe allowed | Monthly |
| Hot sentinel outlets, non-circulating systems | At least 50 °C within one minute (55 °C in healthcare premises) | Monthly |
| Subordinate loop returns, or the last outlet on each loop | Over 50 °C within one minute at the outlet (55 °C in healthcare premises) | Quarterly, ideally on a rolling monthly rota |
| Cold sentinel taps | Below 20 °C within two minutes | Monthly |
| Point-of-use heaters up to 15 litres | 50–60 °C (55 °C in healthcare premises), or a high turnover confirmed | Monthly to six-monthly, or as the risk assessment says |
The log, with a worked example
An office with one calorifier, two principal loops, three subordinate loops and a roof tank. This is the March sheet, filled in on the monthly visit.
| Ref | Point | Target | Time run | Reading | Within target | Action |
|---|---|---|---|---|---|---|
| CAL-1 flow | Calorifier flow | 60 °C or more | – | 61 °C | Yes | – |
| CAL-1 return | Calorifier return | 50 °C or more | – | 55 °C | Yes | – |
| HWS-A | Loop A return leg, 3rd floor riser | 50 °C or more | – | 53 °C | Yes | – |
| HWS-B | Loop B return leg, ground floor east | 50 °C or more | – | 47 °C | No | Reported to the responsible person the same day; return valve on loop B to be checked |
| HWS-SUB-2 | Subordinate loop 2, last basin, kitchen (this month's rota) | Over 50 °C within 1 min | 40 s | 52 °C | Yes | – |
| C-NEAR | Cold tap nearest the tank, 3rd floor tea point | Below 20 °C within 2 min | 2 min | 14 °C | Yes | – |
| C-FAR | Cold tap furthest from the tank, ground floor cleaner's sink | Below 20 °C within 2 min | 2 min | 18 °C | Yes | – |
The CSV file has the same columns plus site, month, who checked, who it was reported to and the date. Rename the references to match the building's schematic and add a row for every sentinel the risk assessment names.
Taking the readings
- Work from the sentinel list in the building's risk assessment or written scheme, not from memory.
- For outlets, run the water and watch the thermometer. Note the time it takes to reach the target, or the reading at one minute (hot) or two minutes (cold).
- On cold taps, watch the reading while the water runs. HSE says this helps "identify any local heat gain, which might not be apparent after one minute" (Table 2.1).
- For return legs, HSE allows readings "on the surface of metallic pipework" (Table 2.1).
- Where an outlet has a thermostatic mixing valve (TMV), the spout gives blended water, typically 38 °C to 46 °C (HSG274 Part 2, para 2.74). A reading there does not show the hot supply. Take the reading at the point the written scheme names for that outlet, and do not record the blended temperature as a failed hot reading.
- Write the reading down at the outlet, with the time run and your name or initials. HSE asks for each record to show who took it, verified by a signature or an electronic equivalent, the date, and enough detail of the location to read the same point again (para 2.54).
When a reading misses the target
The written scheme should set out the "remedial measures to take in case the control limits are exceeded, including lines of communication" (L8, para 62). Follow it. A competent person should interpret the results, and remedial work should be done promptly (L8, para 69).
For a slow subordinate loop outlet, Table 2.1 says to confirm "that the outlet is on a long leg and not that the flow and return has failed in that local area". If readings keep failing, that is a reason to review the risk assessment: "the results of checks indicating that control measures are no longer effective" is one of the triggers HSE lists (L8, para 47). See Legionella risk assessment review.
Who does what
- The dutyholder (the employer, or whoever is in control of the premises) owns the risk assessment and the written scheme, and appoints a responsible person for day-to-day control (L8, paras 28 and 51).
- The contractor takes the readings on the monthly visit, if that is what the contract says. L8 allows monitoring by "an external contractor or an independent third party" (para 65). Report failures straight away, through the route the written scheme sets.
- The responsible person decides on remedial action with the competent adviser and keeps the log with the site's records.
What to record, and for how long
L8 says records should include "the results of any monitoring inspection, test or check carried out, and the dates" (para 71), and that these records are kept "for at least five years" (para 72). A completed monthly log is one of those records. Keep the sentinel list and schematic with it, so the next person reads the same outlets.
Build your own temperature log in the form builder
Field Suite has no ready-made Legionella form yet. You can build this log yourself in the form builder:
- a repeating group with one row per outlet: reference and location (text), hot or cold (choose one), time run (number, seconds) and temperature (number, °C);
- a pass/fail question in each row, "Within target". A fail answer marks the form failed and alerts the office. Number fields do not fail on a limit by themselves, so the engineer answers this against the target printed in the question;
- action taken and reported to (long text), and the site contact's signature.
Attach the form to a contract visit that repeats every month. A job to book is created a set number of days before each visit is due, with the form ready on the engineer's phone. The signed log is kept as a PDF with the job. See planned maintenance software or book a demo.
For the full list of checks behind this log, read Legionella checks for hot and cold water systems. If the same site has pumps, use our pump service checklist.
Questions
Which outlets are the sentinels?
The building's risk assessment should name them. HSE's starting point is the nearest and furthest outlets from the tank or calorifier and the return legs of each loop, with extra outlets for parts of the system those do not represent (HSG274 Part 2, paras 2.59 to 2.63).
Is 55 °C needed instead of 50 °C?
Table 2.1 sets 55 °C for hot outlets and loop returns in healthcare premises, which should also follow Health Technical Memorandum 04-01. Elsewhere the Table 2.1 figure is 50 °C. Care homes and other settings with people at high risk need particular consideration (HSG274 Part 2, para 2.2), so use the target in the building's written scheme.
Can the readings be taken less often than monthly?
Table 2.1 gives monthly for sentinels. HSE says the risk assessment should define the frequency of monitoring for the building (para 2.79), so follow what it says.
Why does the CSV open with odd characters?
It is saved as UTF-8 so the degree sign shows correctly. Open it with File, Import in your spreadsheet and choose UTF-8 if the symbols look wrong.
Field Suite is job management software, not a water hygiene consultancy. The building's own risk assessment and written scheme decide which outlets are read, the targets and how often.
Sources
- HSE, Legionnaires' disease: Technical guidance, HSG274 Part 2 (second edition, 2024), paras 2.2, 2.54, 2.59, 2.62, 2.63, 2.64, 2.74, 2.79 and Table 2.1. https://www.hse.gov.uk/pubns/priced/hsg274part2.pdf
- HSE, L8 Approved Code of Practice and guidance (fourth edition, 2013), paras 28, 47, 51, 62, 65, 69, 71 and 72. https://www.hse.gov.uk/pubns/priced/l8.pdf
Last checked: 5 November 2026 against the sources above.
Field Suite is job management software for UK building services firms, not a consultancy. Your own risk assessments, contracts and advisers decide what applies to your work. Spotted a mistake? Email info@fieldsuiteapp.com and we correct it.