HTM 04-01 and D 08: how TMVs should be tested

Which documents are we talking about?

HTM 04-01, Safe water in healthcare premises, is the Department of Health's guidance for water systems in NHS and other healthcare buildings. It comes in three parts: Part A covers design, installation and commissioning; Part B covers operational management; Part C deals with Pseudomonas aeruginosa in augmented care units.

Alongside those sits a supplement, Performance specification D 08: thermostatic mixing valves (healthcare premises), currently the 2017 edition. Most of D 08 is laboratory testing that manufacturers go through to get a valve TMV3 certified. The bit you need on site is Chapter 11, commissioning and in-service tests, plus Annex F on how often to test.

Part B ties them together. It says thermostatic mixing devices should only go in where a risk assessment shows they're needed (7.40), and that their temperature settings and operation must be checked regularly in line with Chapter 11 of D 08 (6.36 and 7.41). It also points out that local water quality will affect how often valves need maintenance.

Does it apply to you?

Strictly, HTM 04-01 is written for healthcare premises. If you run an NHS site or a private hospital or clinic, your Water Safety Group will expect it. Care homes, supported living, schools and housing providers aren't directly covered. Plenty of them still use the D 08 test as their method, because it's clear and repeatable and an inspector or insurer will recognise it. HSE's HSIS6 also says Type 3 valves should be used in health and social care when TMVs are replaced or newly installed.

Commissioning: setting the baseline

Commissioning (D 08 clause 11.1) is the first test, done when a valve is installed or replaced. The engineer checks the valve is right for the outlet and the supplies are suitable, sets the mixed temperature and makes sure the pipework is free of debris. They then run the same sequence as an in-service test, below. Those first readings are the baseline every later test is compared with, so if your valves were never commissioned on paper, the first service effectively becomes the baseline. There's more in our post on commissioning a new TMV.

The in-service test, step by step

Clause 11.2 of D 08 sets out the routine test. Its purpose, in the document's words, is to maintain assured performance and keep records of how the valve performs. This is the sequence we follow at each valve:

1. Check the supplies. Record the hot and cold supply temperatures next to the valve, and the pressures where they can be measured.
2. Measure the mixed temperature. Run each outlet at maximum available flow and record the temperature at the point of discharge. If needed, adjust it, but never above the Table 17 maximum.
3. Isolate the cold supply. Shut off the cold to the valve and watch the outlet.
4. Apply the 5 second rule. If water is still flowing after 5 seconds, collect it in a measuring jug for 60 seconds. More than 120 ml means the valve needs recommissioning or service work.
5. Restore and re-measure. Turn the cold back on, wait 15 seconds and record the mixed temperature again.
6. Apply the 2°C rule. That reading should be within 2°C of the one taken in step 2. If it isn't, recheck the supplies and recommission the valve to the manufacturer's instructions.
7. Check the strainers and isolators. Note whether strainers and check valves are clean and isolation valves are fully open.
8. Record and set the next date. Write down the final temperature, any work done and when the next test is due.

If a valve fails, the usual causes are scale, debris in the strainer or a tired cartridge. Our post on what to do after a failed fail-safe test goes through the options.