Every TMV reaches a point where you have to ask the question. It's been serviced, recalibrated, given a new cartridge, and it's still giving trouble. Is it worth another repair, or is it time for a new valve?
There's no fixed age when a TMV must be replaced. Plenty of well-made valves keep going for many years with regular servicing, and some fairly young ones turn out to be a poor fit from day one. So rather than going by age, we look at a handful of practical questions.
When repair makes sense
Most of the time, a misbehaving TMV can be repaired. The parts that wear or scale up, mainly the thermostatic cartridge, seals, strainers and check valves, are designed to be replaced. A service kit and a proper clean will bring a lot of valves back to good working order.
Repair is usually the right call when:
- The valve is certified for the way it's being used.
- Parts and service kits are still available.
- The body is in good condition, with no cracks, heavy corrosion or damaged threads.
- The problem is a one-off, or there's a clear cause like scale or debris that servicing fixes.
- The valve is in a sensible position, close to the outlet and reachable for testing.
If all of those are true, a repair is normally quicker and cheaper than replacement, and the valve should carry on happily.
Signs it's time to replace
Parts aren't available any more
Manufacturers update their ranges, and older models eventually lose support. If the cartridge or service kit can't be sourced, the valve can't be properly repaired. Patching it with parts that weren't made for it isn't a sensible option for a safety device.
It keeps drifting despite servicing
A valve that needs recalibrating at every visit, even after a new cartridge, is telling you something. Each callout costs money, and each period of drift is a period where the outlet isn't as safe as it should be. Your test records will show the pattern. We cover the usual causes in why TMV outlet temperatures drift.
It keeps failing the fail-safe test
If a valve fails its fail-safe test, gets repaired, and fails again soon after, it's no longer one to trust. That's the test that matters most, so repeated failures are a strong reason to replace.
It's the wrong valve for the users
Buildings change use. A TMV2 valve that was perfectly reasonable in a general needs flat may not be suitable once that flat becomes supported housing for older tenants. The valve might work fine and still need replacing with a TMV3-certified one. Our guide to TMV2 vs TMV3 explains the difference.
It's in the wrong place
Some older installations have a TMV a long way from the outlet, or one valve serving several outlets. That leaves a long run of warm, blended water, which is a Legionella concern under HSG274. Some valves are buried behind tiled panels where nobody can test them. If the position is the problem, a replacement in the right place is often the better answer than repairing a valve that'll still be awkward and risky.
The body is damaged or badly scaled
Cracks, weeping joints, heavy corrosion or a body so scaled up that parts can't be removed without damage are all good reasons to stop repairing and replace.
Thinking about the cost honestly
Replacement costs more on the day. But it's worth comparing it with the cost of keeping an unreliable valve going: repeated callouts, parts, staff time spent managing outlets taken out of use, and the risk that comes with a valve you can't fully trust.
If several valves on the same site are getting to that stage, it can make sense to plan replacements together rather than one at a time. You get a consistent valve type, one set of spares, and a single disruption rather than many. Spring, before summer refurbishment programmes get booked up, is a good time to get those plans in place.
What a good replacement looks like
If you do replace, make it count. A new TMV should be:
- Certified for the job: the right scheme (TMV2, TMV3 or both) for the users, the outlet and the system pressures.
- As close to the outlet as practical, to keep the run of blended water short.
- Easy to get at, with isolation valves and accessible strainers, so testing and servicing are quick.
- Properly commissioned, with the set temperature recorded and a fail-safe test done on day one. We've written about what commissioning should involve.
- Added to your register, with its early in-service tests booked.
A typical scenario
Imagine a nursing home with around twenty basin TMVs fitted during a refurbishment many years ago. The records show the same valves being recalibrated at nearly every test, and the manufacturer no longer makes cartridges for that model. A sensible plan would be to replace them in batches, a corridor at a time, with a current TMV3 valve fitted close to each basin. Each one is commissioned, labelled and added to the register, and the home ends up with one valve type and one set of spares.
Get a second opinion
If you're not sure, ask whoever tests your valves to look back over the records. A valve's history usually makes the answer fairly obvious. For more on choosing and fitting new valves, see our TMV installation and replacement page, or read about our servicing and repairs.
Not sure whether to repair or replace?
Tell us about the valves and what's been going wrong. We'll give you a straight answer and a clear quote for either option.