# How often should medical gas zone valves be operated and checked?

**How often should medical gas zone and line isolation valves be operated and checked so that they close when needed?**

Under HTM 02-01 (2026), the NHS England guidance, maintenance frequencies, zone valves (AVSUs) included, should be set from equipment manuals with the HTM: closure is tested at validation and may be retested after work, and AVSUs to areas with emergency manifolds should be closed in tests at a frequency agreed with clinical and nursing colleagues.

HTM 02-01, NHS England's guidance for medical gas pipeline systems, calls zone valves area valve service units (AVSUs), which its sample standard operating procedure describes as locked boxes at the entrance to wards and departments whose isolating valves provide both routine and emergency isolation of gas supplies. Line isolation valves are line valves (LVs) and line valve assemblies (LVAs); see [what is a line valve](https://library.ultracontrolo.com/answers/what-is-a-line-valve/). Part B says the actual frequency of maintenance routines should be established from the equipment and plant manuals in conjunction with the HTM, and that practical experience with equipment of different manufacturers, coupled with risk assessments and plant history logs, may lead to some frequencies and tasks being varied.

## When the valves are closed and tested

| When | What is checked | Where in HTM 02-01 |
|---|---|---|
| Engineering validation and verification | Form B23 for AVSUs and form B22 for LVs and LVAs: a valve closure test to confirm a full seal in the closed condition and a zoning test to confirm that the valve isolates only the terminal units or zones it is intended to control, along with NIST connector, identification and signage checks. | Part A 19.67 and 19.68 |
| After work on the system | The tests the Authorised Person (MGPS) can list on the permit to work include ACZNIS, which checks that an AVSU holds pressure when closed and feeds the area intended, and VCZNI, the same check for an LVA; a selection, or all, of the listed tests may follow the work, depending on its complexity. | Part B 7.111 and Table 2 |
| Operational tests | At a frequency agreed with clinical and nursing colleagues, the Authorised Person (MGPS) should perform or supervise the closure of AVSU isolation valves to areas supported by emergency supply manifolds, and the operation of the manifolds and their alarms should be confirmed. The systems should then be returned to normal operating mode, and all operational tests should be detailed in the operational policy. | Part B 11.146 to 11.149 |
| Inspection and cleaning | AVSUs should have an agreed cleaning schedule, and a five-yearly internal inspection and clean should be adequate. Labelling should be checked and the orientation of on/off valves rectified, as necessary, for ease of operation; these inspections are required after any works on the system and on a five-yearly rotation. | Part B, maintenance tasks for AVSUs, valves and LVAs (after 11.212) |

## Records, locks and care

- Checklists: AVSUs should be referred to in the equipment checklist by a number that matches the number on the valve, and it is usually convenient to arrange the checklists so that each valve can be recorded as examined, tested or checked under the planned preventive maintenance (PPM) programme. In HTM terms, to test is to operate the equipment and/or use test instruments to make sure it is functioning correctly.
- Permits: the permit to work system applies to any action, such as closing an isolating valve, that restricts the supply; see who can close a medical gas zone valve.
- Avoiding accidental isolation: when inspecting valves, particularly those left unlocked, Part B says great care must be taken to prevent inadvertent isolation of supplies.
- Locks: all AVSUs should be kept locked, with keys under a key control system; valves in ducts should be kept locked in the normal operating condition, and valves in plantrooms that are not on the plant should be locked.
- Staff: relevant staff should be trained and familiar with the purpose of AVSUs and their correct use in an emergency.
- Faults: where adjustments or other remedial actions are required, they should be carried out at the time, or noted and reported to the Authorised Person (MGPS) when that is not possible, for example when parts are needed.

### Does closing a zone valve for a test need a permit?

Yes. HTM 02-01 (2026) applies the permit to work system to any action, such as the closure of an isolating valve, that restricts the supply.

### What does an AVSU closure test check?

Under HTM 02-01 (form B23), that the valve achieves a full seal in the closed condition; the zoning test confirms that it isolates only the terminal units or zones it is intended to control.

## Sources

- [NHS England, HTM 02-01 Medical gas pipeline systems, Part B (2026), paras 6.34, 7.7, 7.111, 11.108 to 11.110, 11.114, 11.146 to 11.149, 11.208, 11.211, 11.212 and its task list, Table 2 and Appendix B (sample SOP)](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)
- [NHS England, HTM 02-01 Medical gas pipeline systems, Part A (2026), paras 19.67 and 19.68](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)

Reviewed: 2026-10-23. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-often-should-zone-valves-be-operated-and-checked/