TMV Risk Assessment: Scalding and Legionella Checks
A TMV risk assessment decides where thermostatic mixing valves are needed on your site, what temperature each one should deliver, and how often it must be tested and serviced. It has to weigh two risks at once. Hot water stored and distributed hot protects against Legionella, but hot water at the outlet can scald vulnerable people. The assessment sets out how you control both, and the records prove it.
TL;DR
A TMV is there to deliver safe water at the outlet. It does not control Legionella, so the wider hot water system still has to be managed.
Risk assess by person and outlet: who uses the water, how vulnerable they are, and whether the outlet is a bath, shower or basin.
Where vulnerable people bathe or shower, HSE says water must not exceed 44°C. Test valves at least annually, or more often if the assessment says so.
Keep records of who tested what, when, the results and any corrective action, for at least five years.
A failed valve is serviced or adjusted to the manufacturer’s instructions and then re-commissioned, not simply left in use.
Table of Contents
What a TMV risk assessment covers
A thermostatic mixing valve blends hot and cold water to a set outlet temperature. Many sites need them because Legionella control pushes system temperatures up. HSE guidance says hot water should be stored at 60°C or above and distributed at 50°C or above to control the bacteria, and temperatures over 44°C create a scalding risk to vulnerable people.
Those two numbers pull against each other. The TMV risk assessment is where you reconcile them. It normally answers five questions:
Who can reach each outlet, and are they vulnerable to scalding?
Which outlets need a TMV, and which are adequately controlled another way?
What outlet temperature should each valve be set to?
How will you commission, test and service the valves?
What will you record, and what happens when a result fails?
It works best as part of your wider Legionella risk assessment, not as a separate document. Our Legionella risk assessments look at the whole water system, with the TMV schedule inside it, so the two risks are reviewed together.
A TMV is not a Legionella control
This point catches out many dutyholders. The BEAMA and Kiwa guidance makes clear that TMVs are a means of delivering water safely for user comfort, not a way of managing Legionella. The pipework downstream of a valve holds warm water, so the valve itself and the pipe run to the outlet need to be part of your control scheme. Treat the valve as a possible risk point as well as a safety device.
Step 1: Work out who is at risk
Scalding risk is about people before it is about plumbing. The same basin can be low risk in an office and high risk in a care setting.
HSE’s guidance for health and social care points to a vulnerability assessment covering mental capacity, mobility and sensitivity to temperature. In practice, think about:
Children and young people, such as in schools and nurseries.
Older people and those with reduced mobility, who cannot move away quickly from hot water.
People with reduced sensation, for example through diabetes or neurological conditions.
People with cognitive impairment, who may not recognise or react to danger.
Anyone who cannot control the water independently, such as a person being bathed by staff.
HSE also advises that where residents are in an ‘at risk’ group for infection, such as immunocompromised people, an assessment should classify them accordingly. One person can be vulnerable to both risks, which is why the two sides of the assessment cannot be done in isolation.
Step 2: Decide where TMVs are needed
The risk depends on the outlet as much as the user. HSE’s position is straightforward:
Outlet | Scalding risk | What HSE guidance says |
Bath | Highest: whole body immersion | Water must not exceed 44°C where vulnerable people are at risk |
Shower | High | Fit TMVs where storage and distribution temperatures are used for Legionella control |
Hand wash basin | Lower | Minimal where water is delivered up to 50°C, but vulnerable users may still need TMV control |
Electric shower | Depends on output | Check potential output under varying pressure and flow |
The detail comes from two HSE pages. For baths and showers where 60°C storage and 50°C distribution are used, thermostatic mixer valves should keep temperatures at or below 44°C, and the outlet temperatures and valves should be monitored and maintained. For basins, HSE notes that a hot water warning notice may be sufficient where scalding risk is minimal, though basins used by people assessed as vulnerable need output controls such as TMVs.
For NHS premises, HSE notes a lower maximum of 41°C for electric showers, and healthcare-standard units may be needed if a shower could exceed 44°C. Hospitals and care homes also follow the specific healthcare technical guidance, so check which standard applies to you.
Common outlets to include in the survey
Showers and baths in care homes, sheltered housing and healthcare wards
Basins in toilets, treatment rooms and consulting rooms where vulnerable patients wash
School and nursery washrooms
Accessible and disabled toilets
Hotel and leisure facilities with showers in public areas, which we cover in our guidance on hospitality and leisure premises
The aim is a written, outlet-by-outlet decision: TMV fitted, TMV needed, or no TMV needed with a reason. Include the ones you decide against, because an auditor will ask.
Step 3: Set and verify the right temperatures
The valve protects the user, but the water feeding it must still do its job for Legionella control. HSE guidance says the hot water at the inlet to the TMV should reach at least 50°C within one minute of running. If it does not, you may have a circulation or balancing problem upstream. We explain how to approach that in our article on hot water returns below 50°C, and our summary of HSG274 temperature limits sets out the 60°C and 50°C benchmarks in plain terms.
On the outlet side, the target is the blended temperature agreed in the assessment for that type of outlet, within the 44°C ceiling for bathing. The commissioning result then becomes the baseline for every later test.
Equipment for testing
Use the right thermometer, or the readings are not worth recording. BEAMA guidance recommends calibrated digital thermometers with a refresh rate of at least four times per second, and says liquid-filled thermometers must not be used. A valve can settle and drift within seconds, and a slow instrument misses it.
Step 4: Commission and test in service
Installation, commissioning and testing of valves should follow the manufacturer’s instructions and relevant standards. Commissioning records the valve’s starting performance. Without them, nobody can say later whether a valve has drifted.
In-service testing compares the valve with that baseline. Kiwa guidance for Type 2 valves says they should be tested against their commissioning results once a year. The test checks two things:
the mixed outlet temperature remains stable, within ±2°C of the commissioning result;
the valve fails safe, so flow stops or is limited when the cold supply is isolated.
If you need a fuller picture of what an annual or six-monthly regime looks like, see our guide to TMV servicing requirements in England.
How often: let the assessment decide
Annual testing is the floor in the guidance above, not a ceiling. The risk assessment should set a shorter interval where:
the outlet serves highly vulnerable users;
the water is hard, or scale or debris has caused valve problems before;
previous tests have failed;
the valve is old or its service history is incomplete.
In augmented care settings the Department of Health treats operating procedures such as daily flushing of infrequently used taps and regular TMV servicing as vital layers of defence against opportunistic pathogens such as Pseudomonas aeruginosa. Our article on Pseudomonas in water systems explains how that connects to water sampling in healthcare.
Where a building management system is installed, HSE notes it could be used to carry out these temperature measurements. If you manage many outlets, automated temperature monitoring can reduce the manual rounds and show trends between visits.
Step 5: Record everything and act on failures
A test nobody wrote down did not happen, as far as an auditor or investigator is concerned. HSG274 Part 1 says records should identify who did the work and when, with the results and any corrective actions, and that monitoring and inspection records should be kept for at least five years.
A useful TMV record has these fields:
outlet location and unique valve reference;
valve type and manufacturer;
date, name and competence of the person testing;
inlet hot and cold temperatures, and the mixed outlet temperature;
result of the cold-water isolation (fail-safe) test;
pass or fail against the commissioning baseline;
action taken and the date it was closed out.
If you want a template, our temperature monitoring checklist and our walkthrough on completing temperature monitoring checks show the layout.
When a valve fails
If a valve fails an in-service test, because the temperature is outside the set range or the shut-off is inadequate, Kiwa guidance says it must be serviced or adjusted to the manufacturer’s instructions and then re-commissioned. In practice:
Record the failed result as found, before touching the valve.
If vulnerable people use the outlet, take it out of use or restrict access until it is fixed.
Service, clean, descale or replace the valve as the manufacturer specifies.
Re-test and re-commission, and record the new baseline.
Ask why it failed. A pattern across many valves points to a system problem, not a faulty part.
Perspective
Most of the TMV paperwork we see fails in the same place: the valve was assessed on its own, and the system around it was not. A dutyholder has a neat annual service sheet, but nobody has checked that hot water reaches the valve at 50°C, or that the pipe after it is used often enough to stay fresh. Our approach is to make the TMV schedule part of the Legionella risk assessment, so one document answers both questions: who could be scalded, and where could bacteria grow. We write the schedule outlet by outlet, give each a reason, and set test frequencies to the site, not a generic default. That is what we mean by bespoke compliance. A care home, a school and a hotel carry different risks, and their TMV regimes should look different. If your register is a spreadsheet that has not been challenged for years, a fresh look at outlet vulnerability and test intervals is usually the most valuable hour you can spend. Sammi
How we can help
We assess the whole water system, schedule TMVs against the vulnerability of the people using each outlet, and carry out the testing and servicing. Our Legionella risk assessments start from £185, and we cover the service and repair side through our TMV servicing and remedial works.
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If you are not sure what your current assessment says about valves, send it over and we will tell you what we would expect to see. Where valves have failed or water temperatures are consistently out of range, our system disinfection and flushing team can deal with the downstream consequences, and our training courses help your in-house staff run the checks properly.
Who should carry out a TMV risk assessment
The dutyholder is responsible, and may be the employer, the landlord or the person in control of the premises. They must appoint someone competent to do the work, which means a person with the training and experience to understand both the Legionella and the scalding questions. A plumber who can service a valve is not necessarily able to judge whether an outlet is suitable for a vulnerable group.
When choosing who does it, look for:
a written scope that covers outlet vulnerability, not just valve servicing;
thermometers calibrated and traceable;
reports with outlet-level actions, priorities and timescales;
a clear link between the TMV schedule and your written scheme and logbook.
When to review the assessment
Do not leave the assessment on the shelf. Review it when:
the building, its use or its users change, for example a wing converted to residential care;
pipework, heaters or valves are altered or replaced;
tests show repeated failures;
a Legionella or Pseudomonas sample result is positive;
a scalding incident or near miss occurs.
After a positive sample, sampling and analysis help confirm whether the problem is localised. Our water testing and analysis service starts from £55 per sample.
FAQ
Does every tap need a TMV?
No. The need is decided outlet by outlet in the risk assessment. HSE says scalding risk at basins is lower, and a warning notice may be enough where water is up to 50°C, but baths, showers and basins used by vulnerable people need controls.
What is the maximum temperature for a bath or shower?
Where vulnerable people are at risk during whole body immersion, HSE says water must not exceed 44°C. For electric showers in NHS settings, the stated maximum is 41°C.
How often should TMVs be tested?
At least once a year for in-service testing against the commissioning results, according to Kiwa guidance. The risk assessment can set a shorter interval for high-risk outlets, valves with a poor history or hard water areas.
Can a TMV prevent Legionella?
No. It is designed to deliver safe outlet temperatures, not to control bacteria. Legionella control still depends on correct storage and distribution temperatures, flushing and the wider water management plan.
How long do we keep TMV records?
HSG274 says monitoring and inspection records should be kept for at least five years. They should show who did the work, when, the results and any corrective action.
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