What is a TMV?

A TMV (thermostatic mixing valve) mixes hot and cold water so it comes out at a safe temperature - usually 38 to 41 degrees C. This stops people getting scalded.

How It Works

Inside the valve, a special part shrinks and grows as the water temperature changes. This automatically adjusts the mix of hot and cold water to keep the temperature steady.

If the cold water stops flowing, this part shuts off the hot water too. This is called the failsafe - it stops scalding water reaching the tap.

How to Service It

1. Turn off both the hot and cold water to the valve.
2. Open the tap to release pressure and drain water.
3. Take off the cover.
4. Remove and clean the strainers (these catch dirt).
5. Check the one-way valves (check valves) - replace if worn or scaled.
6. Check the temperature part (thermostatic cartridge) - replace if damaged or if it is due.
7. Clean everything and descale if needed.
8. Put it back together with new seals.
9. Turn the water back on and wait 2-3 minutes.
10. Set the temperature to 41 degrees C max using the adjustment cap.
11. Test the failsafe: Turn off the cold water only. The hot water should stop within 2 seconds. If it does not stop, the valve is broken - replace the cartridge.
12. Write down the temperatures, failsafe test result, and what parts you replaced.

Common Problems

• Temperature keeps changing: The temperature part is failing or scaled. Replace it.
• Failsafe does not work: Replace the cartridge. Check for dirt stopping the valve from closing.
• Low water flow: Clean or replace the strainers and check valves.
• Temperature goes up and down: Check if hot and cold water pressures are different. Check the one-way valves.

How Often to Service

• Once a year (minimum)
• Twice a year in hospitals and care homes
• Within 30 days of installing a new one