It's one of the first questions we get asked, and the honest answer is "it depends". That's not us dodging it. The right interval for your valves depends on who uses them, what your water is like and how the valves have behaved so far. But there is a sensible way to work it out, and it isn't complicated.
The short answer
Every TMV should be tested at least once a year. In care homes, hospitals and other places where the people using the water are vulnerable, every six months is common. Some valves need checking more often than that if they keep drifting.
Brand-new valves are a special case. They should be checked within the first few months after they're fitted, before you settle on a routine.
Where the guidance comes from
The most detailed guidance on TMV testing is in HTM 04-01, the Department of Health and Social Care's guidance on safe water in healthcare premises. It's written for healthcare, but lots of care providers, schools and housing providers follow it because it's practical and well thought through.
Rather than giving one fixed interval for every valve, it takes a results-based approach:
- Commission the valve and record the baseline readings: supply temperatures, mixed temperature and the result of the fail-safe test.
- Test it again in the first few weeks after installation.
- Test it again a few months in.
- Compare the results. If the mixed temperature has hardly moved, you can set a longer interval. If it's shifted noticeably, the valve needs servicing and more frequent checks.
That's the bit people miss. The interval isn't just a date in the diary, it's a judgement based on evidence. A valve that holds its temperature beautifully for two years is telling you something different from one that's crept up three degrees in six months.
Your Legionella risk assessment and written scheme (under ACOP L8 and HSG274) should also cover TMVs, so the frequency for your site may already be written down somewhere. Manufacturers' instructions are worth checking too, as some set their own maintenance intervals.
What pushes the interval shorter
There are a few things that make us suggest testing more often than once a year.
Vulnerable users
Older residents, people with dementia or reduced feeling, patients and very young children can be badly hurt by water that's only a few degrees too hot, and they may not be able to react. For valves serving them, six-monthly testing is a sensible starting point.
Hard water
Limescale is the number one reason we find valves that don't respond properly. In hard water areas, scale builds up on the thermostatic element and in the strainers, and the valve gets sluggish. Regular descaling keeps it working. There's more on this in hard water and TMVs.
A history of drift
If previous records show a valve needing recalibration every time, it's either due for a new cartridge or it needs watching more closely. Sometimes both. We look at the usual causes in why TMV outlet temperatures drift.
Changes to the system
New boilers, a different calorifier set point, pump changes or major pipework alterations can all upset the balance of supply temperatures and pressures that a TMV relies on. It's worth testing affected valves after any significant change.
What pushes it longer
Where users aren't particularly vulnerable, the water's soft and a valve has a clean, stable track record over several tests, annual testing is usually reasonable. We wouldn't go longer than that. A year is a long time for a valve to go unchecked.
A typical scenario
Imagine a care home with around thirty TMVs: a mix of assisted baths, en-suite showers and residents' basins. The previous contractor tested everything once a year, and the records show a handful of basin valves needing recalibration at nearly every visit.
A sensible plan would be to move the whole home to six-monthly testing, given the residents. The repeat offenders would get new cartridges, then be watched at the next couple of visits to confirm they're holding. And any new valves fitted would get their early checks booked in straight away so they don't get forgotten.
That's not a dramatic change, but it means problems get caught within months rather than up to a year later.
Testing versus servicing
People use these words loosely, so it's worth separating them.
- Testing means measuring the supply and mixed temperatures and doing the fail-safe test (isolating the cold supply to check the valve shuts down).
- Servicing means the hands-on work: cleaning strainers and check valves, descaling, recalibrating and replacing worn parts.
At every visit we test. Whether a valve also needs a full strip-down depends on what the test shows and how long it's been. Either way, the results go against that valve in your asset register, so the next visit starts with a clear picture.
Don't wait for the date if something feels off
Whatever your interval, if someone reports a shower running hotter than usual, water surging hot and cold, or a weak flow from a TMV outlet, get it checked. If a valve has failed its fail-safe test, take that outlet out of use until it's fixed.
Getting it organised
The hardest part for most sites isn't knowing the interval, it's remembering it. Valves get installed, the early checks get missed, and two years later nobody's sure when anything was last tested. That's exactly why we schedule visits and send reminders before tests fall due.
If you'd like us to look at your current records and suggest a sensible schedule, we're happy to. See what's included in a TMV service, or read our TMV compliance guide for more on HTM 04-01.
Want us to take a look at your valves?
Tell us roughly how many TMVs you've got and where you are. We'll come back with a clear, fixed quote.