Health Technical Memorandum 04-01 Supplement: Performance Specification D 08 – Thermostatic Mixing Valves in Healthcare
Health Technical Memorandum 04-01 Supplement: Performance specification D 08: thermostatic mixing valves (healthcare premises) is a technical performance standard issued by the Department of Health in the United Kingdom. Published in its 2017 edition (March 2017), the document functions as a supplement to the broader HTM 04-01 framework, which includes Part A (Design, installation, and testing), Part B (Operational management), and the Addendum regarding Pseudomonas aeruginosa. It establishes the criteria for the design, manufacture, and verification of thermostatic mixing valves (TMVs) intended for use in high-risk healthcare and social care environments.
The scope of this specification covers Type 3 thermostatic mixing valves with a nominal size up to and including DN 25. It defines rigorous requirements for construction materials, leaktightness, durability, and thermal performance across various applications, including bidets, showers, washbasins, and baths. The document is structured into technical chapters covering Construction (3.0), Sampling (4.0), Leaktightness (5.0), Durability (6.0), and Performance (7.0). It also details mandatory Commissioning and in-service tests (11.0) required to maintain safe water temperatures for Vulnerable people, specifically defined to include children, older people, and those with reduced mental capacity or temperature sensitivity.
This specification serves as the primary reference for manufacturers seeking Type 3 approval, as well as for engineers and estate managers responsible for the installation and maintenance of water systems in hospitals and care homes. It incorporates normative annexes describing the specific test rigs and apparatus required for durability and performance verification.
Scope and Operating Conditions
The specification applies to thermostatic mixing valves installed for ablutionary purposes where the risk of scalding must be minimized. Operating conditions are categorized into High pressure and Low pressure ranges, with a maximum static pressure of 10 bar for both.
- High pressure flow pressure: 1 to 5 bar (hot and cold).
- Low pressure flow pressure: 0.2 to 1 bar (hot and cold).
- Supply temperatures: Hot water at 55°C to 65°C; cold water at 5°C to 20°C.
- Mixed water temperature limits: Bidet (38°C max), Shower and Washbasin (41°C max), Bath fill (44°C or 46°C max).
Type 3 Certification Scheme Requirements
To comply with HTM 04-01: Supplement, manufacturers must adhere to a strict third-party certification scheme. This ensures that the valves are not only designed to high standards but also consistently perform over their operational lifespan.
- UKAS Accreditation: Certification organizations and test houses must be accredited against BS EN ISO/IEC 17065 and BS EN ISO/IEC 17025 respectively.
- Approval Period: Type 3 approval is valid for five years, after which a full re-test is mandatory.
- Performance Audits: Approved valves must undergo performance audits twice within the five-year approval period.
- Quality Systems: Manufacturers are required to maintain a UKAS-recognised ISO 9001 quality system.
Construction and Material Standards
Chapter 3.0 specifies that all materials in contact with water must satisfy safety criteria to prevent contamination and ensure mechanical integrity.
- BS 6920 Compliance: All non-metallic materials must comply with BS 6920 for their effect on water quality.
- WRAS Approval: Materials should follow the Water Regulations Advisory Scheme (WRAS) material guidance.
- Removable Devices: Any flow rate regulators intended for removal during commissioning must be supplied fitted to the valve.
Testing Protocols and Durability
The document outlines specific laboratory type tests that three random samples (denoted A, B, and C) must pass to meet the performance specification.
- Leaktightness (5.0): Verification of the obturator and the complete mixing valve at pressures up to 16 bar.
- Durability of on/off control (6.1): Valves must withstand 50,000 on/off cycles under specified pressure and temperature conditions.
- Thermostat Durability (6.3): Requires 30,000 cycles of accelerated operation representative of normal use.
- Thermal Shut-off (7.9): Assessment of the valve's ability to isolate flow rapidly in the event of a cold or hot water supply failure.
Commissioning and In-service Testing
Chapter 11.0 and Annex F provide the procedure and frequency for on-site testing to maintain performance after installation.
- Commissioning Procedure: Includes recording supply temperatures/pressures and performing a cold water supply isolation test.
- Initial In-service Test: Conducted six to eight weeks after commissioning.
- Second In-service Test: Conducted twelve to fifteen weeks after commissioning.
- Maximum Deviation: If mixed water temperature deviates by more than 2°C from the set temperature, the valve must be rechecked or recommissioned.
Frequently Asked Questions
What is the maximum permitted mixed water temperature for a healthcare shower?
According to Table 2, the maximum mixed water temperature at the point of discharge for a shower (designation S) is 41°C.
How are vulnerable people defined in this specification?
Vulnerable people are defined as children, older people, individuals with reduced mental capacity, mobility, or temperature sensitivity, and those who cannot react quickly enough to prevent injury.
What is the required frequency for in-service testing of TMVs?
Initial tests are performed at 6-8 weeks and 12-15 weeks after commissioning. Depending on results (deviation ≤1 K), subsequent intervals may be set between 18 and 28 weeks as detailed in Annex F.
What happens if a TMV fails the cold water isolation test during commissioning?
If there is a flow stream after 5 seconds, the volume collected in 60 seconds must not exceed 120 ml. If it exceeds this volume, further investigation, service work, or recommissioning is required.
Which British Standards are relevant to the testing of TMVs in this memorandum?
Relevant standards include BS EN 1111 (High pressure TMVs), BS EN 1287 (Low pressure TMVs), and BS 6920 (Materials in contact with water).
Is a thermal shut-off test required for all Type 3 valves?
Yes, thermal shut-off is a core performance requirement detailed in clause 7.9 to ensure safety in the event of a supply failure.
What is the maximum static pressure allowed for TMVs in healthcare premises?
Table 1 specifies a maximum static pressure of 10 bar for both high and low operating pressure ranges.
How long is a Type 3 TMV approval valid?
Type 3 approval is issued for a period of five years, after which the valve must undergo a full re-test for recertification.
