60°C storage, 50°C outlets: HSG274 limits for England dutyholders
The HSG274 Part 2 temperature limits are clear: cold water should stay below 20°C, hot water must be stored at 60°C or above, and hot water must reach 50°C at outlets within one minute, rising to 55°C in healthcare premises. These figures exist because Legionella multiplies between 20°C and 45°C. HSG274 is guidance supporting ACOP L8, and your site-specific risk assessment governs the final controls you put in place.
TL;DR:
Maintaining hot water at or above 60°C and cold water below 20°C at designated points is essential to prevent Legionella growth in all system parts.
Hot outlets must reach 50°C within one minute of opening, with healthcare settings requiring 55°C, while cold outlets should be below 20°C at sampling points.
Regularly testing sentinel outlets near the calorifier, the furthest points, and stagnation-prone branches ensures system performance and helps detect dead legs or stagnation issues.
Monitoring temperatures with calibrated probes or BMS integration and recording details like date, time, and outlet location is critical for audit compliance.
When temperature targets cannot be met, alternative controls such as chemical biocides or system redesigns must be documented and proven effective through continuous monitoring.
Table of Contents
Why these temperature limits matter for legionella growth
Legionella bacteria multiply fastest in water sitting between 20°C and 45°C. Below 20°C the bacteria become dormant rather than active, and above 60°C they do not survive. That three-way split, dormant, active, non-viable, is the entire logic behind HSG274’s numbers. Cold storage and distribution targets exist to keep water out of the growth window on one side; hot storage and distribution targets exist to push it past the lethal threshold on the other.
The trouble is that most systems create a middle ground somewhere between the two. A cold-water tank in a warm plant room, a length of pipe that never quite reaches its target temperature, a shower head that takes ninety seconds to run hot, these are the lukewarm zones where the growth window opens up in practice, not just in theory.
This is also why storage checks and outlet checks are treated differently under HSG274. A calorifier holding water at 60°C tells you the source is safe. It tells you nothing about what happens over the metres of pipe between that calorifier and a tap that nobody has used for a fortnight. Distribution checks exist precisely because storage temperature and delivered temperature are not the same fact, and a system can pass one test while failing the other.
Where the numeric targets apply across your system
HSG274 Part 2 sets out specific numbers for specific points in a water system, and knowing which number applies where is the difference between a defensible log and a guess.
Hot water storage, meaning the calorifier or hot water cylinder, should sit at 60°C or higher. Flow leaving the calorifier should also be at least 60°C, with the return leg no lower than 50°C, tightening to 55°C in healthcare settings. At the outlet itself, whether that is a tap, shower or sentinel point, water should reach 50°C within one minute of opening (again 55°C in healthcare). Cold water storage and distribution should stay below 20°C wherever the system allows it, with recognised exceptions for combination boilers and low-volume water heaters that do not hold large static volumes.
System component | HSG274 Part 2 target |
Hot water storage (calorifier) | At least 60°C |
Hot water flow | At least 60°C |
Hot water return | At least 50°C (55°C in healthcare) |
Hot outlet, within one minute | At least 50°C (55°C in healthcare) |
Cold water storage and distribution | Below 20°C where practicable |
Our HSG274 Part 2 checklist breaks these targets down into a monthly action plan for facilities teams managing several buildings at once.
Monitoring: sentinel selection and check frequencies
A monitoring programme only holds up under scrutiny if the sentinel points chosen actually represent the system. Sentinels should include the outlet nearest the calorifier, the outlet furthest from it, and any long branch that could stagnate independently. On larger or more complex systems, checking only the nearest and furthest points often misses failing sub-loops in between, so a rotational representative sample across the wider outlet set fills that gap.
Test hot outlets by running water and recording the temperature at one minute using a calibrated probe held clear of the tap body.
Test cold outlets similarly, allowing a longer run time, typically around two minutes, before recording.
Check calorifier flow and return temperatures monthly using fixed sensors or a manual probe at the pocket.
Check cold water storage tanks and incoming mains every six months.
Rotate through the remaining outlets annually so every point on the system is checked within a reasonable cycle.
Pro Tip: Keep a simple site map marking every sentinel point and rotation date, it turns a vague “we check regularly” into evidence an inspector can follow in seconds.
Persistent low readings, evidence of stagnation, or any change to the system, a new extension, a decommissioned wing, a re-routed loop should trigger an investigation rather than another routine check. Our guide on our sentinel outlets page covers how to build that rotation into a defensible monthly schedule.
Managing scald risk with thermostatic mixing valves
Storing water at 60°C and delivering it at 50°C or above protects against Legionella, but it also creates a scald hazard, particularly for children, older residents and anyone with reduced sensitivity to heat. HSE expects a Type 3 thermostatic mixing valve fitted at baths and showers used by vulnerable people, preventing discharge above 44°C at the point of use. For most people, delivery up to 50°C at a hand-wash basin carries minimal scald risk, subject to your own assessment.
The key point that gets missed is that a TMV is a downstream control, not a reason to lower storage temperature. Dropping a calorifier setpoint to make outlets feel safer defeats the entire Legionella strategy upstream of the valve.
Check the temperature entering the TMV, not just the blended output leaving it.
Service and test TMVs on a fixed schedule, since a failed valve can silently drift towards scald temperatures or lukewarm stagnation.
Fit signage where mixed outlets serve vulnerable users, and record the mitigation in the risk assessment.
What kills legionella and corrective steps when readings fail
Legionella does not survive above 60°C, and sustained exposure at that temperature through storage, flow and return is what “thermal control” actually means in practice, rather than a single hot flush fixing a system overnight. Absolute claims about instant kill temperatures at the tap are misleading: what matters is the whole system holding its target consistently.
When a check comes back low, act on the specific fault rather than the symptom. Where it is safe to do so, raise the storage temperature and flush the affected outlet or leg thoroughly. Check balancing valves and pipe insulation on that branch, since a badly balanced loop often explains why one outlet consistently underperforms while others pass. Dead legs, sections of pipe with no regular flow, should be removed where the system allows it, since they are a common source of persistent lukewarm readings.
If flushing and rebalancing do not resolve the issue, or if readings suggest wider contamination, commission a professional disinfection and follow it with water sampling to confirm the fix worked. Record the incident, the corrective action and the retest result in the risk assessment file, since a one-off low reading with no follow-up is exactly what an inspector will query first.
Measuring and recording temperatures for an audit trail
A reading is only as good as the instrument and technique behind it. Use a calibrated immersion thermometer or digital probe for manual checks, and where the site has a building management system, feed calorifier flow and return data into it directly for continuous logging. Calibrate probes against a certified reference on a fixed schedule, not just when a reading looks suspicious.
Run hot outlets for up to one minute before recording, matching the HSG274 performance test rather than switching the tap off early.
Run cold outlets for around two minutes, since cold pipework typically takes longer to clear standing water.
Use the thermometer pocket on calorifiers rather than an open probe in the tank, for a stable and repeatable reading.
Pro Tip: A photo of the probe display next to the outlet, timestamped, turns a paper log entry into evidence nobody can dispute later.
Inspectors expect to see the date, time, outlet reference, reading and initials for every check, plus a clear trail of what happened after any failed reading. Our step-by-step guide on temperature monitoring checks sets out a log format that covers exactly this.
When alternatives to temperature control are acceptable
HSG274 is technical guidance supporting the legal duties set out in ACOP L8, and it is your site-specific risk assessment that decides which controls actually apply on your system. Where strict temperature targets cannot be met, chemical biocides, increased water turnover, or system design changes such as removing oversized dead legs can serve as alternative controls, provided their effectiveness is demonstrated through ongoing monitoring.
Relying on an alternative means documenting why temperature control alone was not achievable, what the substitute control is, and what evidence, chemical residual readings, turnover records, sampling results, confirms it is working. An inspector reviewing the file will expect to see that reasoning recorded, not assumed.
Common site failures and pragmatic fixes
Most non-compliant readings we encounter trace back to the same handful of causes: poorly balanced loops, dead legs left in after refurbishment, and sentinel coverage that skips the outlets most likely to stagnate. None of these need a major capital project to fix, just a proper look at the pipework and a rotation that actually represents the site.
A representative sentinel programme, backed by automated monitoring where the site can justify it, gives you an audit trail that holds up without a fight. If your system needs remedial attention now, specialist compliance services can help.
— Sammi
How Bespoke Compliance Solutions supports your compliance programme
Getting HSG274 targets right across a live site takes more than a thermometer and a spreadsheet, it takes a scope built around how your buildings actually run. Specialist companies work with facilities and healthcare sites across England to close the gap between a temperature log and a defensible compliance file.
[
Our services map directly onto the checks covered in this guide:
Legionella risk assessments to set the site-specific controls HSG274 expects.
Automated water temperature monitoring for continuous calorifier and sentinel readings with an alert trail.
Water testing and analysis when a failed reading needs laboratory confirmation.
TMV servicing and remedial works to fix balancing, dead legs and scald controls.
Disinfection and tank cleaning where remedial action goes beyond flushing alone.
Exact scope and pricing depend on your site, so we start with a survey rather than a quote off the shelf. Book a site visit through our risk assessment page to get your programme moving.
FAQ
At what temperature will legionella begin to be killed by heat?
Legionella does not survive at temperatures above 60°C, which is why HSG274 sets hot water storage at that level or higher. Below 60°C but above 20°C, the bacteria can multiply rather than die off, so consistent storage temperature matters more than a brief spike.
What temperatures are ideal for legionella testing?
Sentinel checks test hot outlets for a reading of at least 50°C within one minute of opening (55°C in healthcare), and cold outlets for a reading below 20°C. These are the reference points HSG274 uses to judge whether a system is performing as designed.
What temperature kills legionella in a boiler or calorifier?
Calorifiers and hot water cylinders should store water at 60°C or above, the threshold at which HSE states the bacteria do not survive. Flow leaving the calorifier should stay at or above that same 60°C figure to maintain the effect through the system.
Is HSG274 law?
HSG274 is HSE technical guidance, not law in itself; it supports the legal duties set out in the Approved Code of Practice, ACOP L8. Your site-specific legionella risk assessment is the document that determines which controls apply on your system.
Recommended
Comments