This page covers Great Britain. The Gas Safety (Installation and Use) Regulations 1998 apply in England, Wales and Scotland. Northern Ireland has its own regulations, which this page does not cover. It sets out what the law and HSE's Approved Code of Practice (L56) say, as at 30 September 2026. It does not give test pressures, times or permitted pressure drops, for the reason explained below.

If you smell gas

Call the National Gas Emergency Service on 0800 111 999 for natural gas. For LPG, call your gas supplier's emergency number, which may be shown on the tank or cylinder.

Under regulation 37, the person responsible for the premises must shut off the gas supply straight away. If gas keeps escaping, or the smell persists, they must report it to the gas supplier at once. The supply must not be turned back on, other than to repair it, until steps have been taken to stop the escape happening again.

L56 adds that you should open doors and windows and avoid anything that could ignite the gas, such as smoking or using electrical equipment. Do not go into a confined space that smells of gas to reach the control valve. Leave the building instead. Regulation 6(5) says no one searching for a gas escape may use any source of ignition.

When a tightness test is a legal duty

The regulations require a gas tightness test in these cases:

After work on installation pipework that might affect its gastightness (regulation 22(1)). The part worked on must be tested straight away to show it is gastight, and examined to show it was installed in line with the regulations.
After work on any gas fitting that might affect the tightness of the installation (regulation 6(6)). The test must reach at least as far as the nearest valves upstream and downstream.
After installing an appliance while gas is supplied (regulation 33(1)). The appliance's connection to the pipework must be tested to show it is gastight.
Before gas is first let into pipework where no gas was being supplied (regulation 22(3)). No one may let gas in until the testing and purging has been done.

"Work" is defined widely in regulation 2. It includes installing, reconnecting, maintaining, servicing, adjusting, disconnecting, repairing, altering, renewing, moving or removing a fitting, and purging it. Connecting or disconnecting a bayonet fitting or other self-sealing connector is not work.

Only a competent person may do this work, and they must be, or work for, a member of a class of persons approved by HSE (regulation 3). In practice that means Gas Safe registration.

What the test must cover

L56 describes the tightness test as the test that confirms the gas system has no escapes. It is also called a soundness test or pressure decay test. In a domestic setting, L56 says the test normally needs to cover the installation pipework from the meter control valve or emergency control valve to the appliance shut-off device (guidance paragraph 125).

L56 also says (ACOP paragraphs 214 to 216):

Visually inspect every joint affected by the work, as part of the test.
Test joints before painting them or protecting them against corrosion. Paint put on first can seal a leak for a while and give a false result.

Only after testing and examination should any protective coating the joints need be applied (regulation 22(1)(b)).

Where the test figures come from

The regulations and L56 do not set test pressures, stabilisation times, test times or how much pressure drop is allowed. L56 says the gastightness requirements are set out in the appropriate standard (guidance paragraph 217, and ACOP paragraph 123).

The figures used in the industry for smaller low-pressure installations come from IGEM/UP/1B, published by the Institution of Gas Engineers and Managers. It is sold rather than published openly, so this page does not repeat its figures. Use the current edition of the standard for the gas and installation in front of you, and the appliance manufacturer's instructions.

Purging and retesting

Where gas is supplied to the premises, regulation 22(2) says that straight after testing:

Purge all installation pipework that gas can now flow through, so that all air and any other gas is safely removed.
If the pipework is not going into use straight away, seal every outlet with the appropriate fitting.
If you purged through a loosened connection, retest that connection for gastightness once you have tightened it.
Test every seal fitted after purging for gastightness.

L56 says purging should follow the appropriate standard and should be done after any work that breaks into the pipework, not only when gas is first supplied (ACOP paragraph 218).

The duty to test and purge on first supply does not apply just because gas was turned off for a while, for example at the emergency control, or because the customer changed gas supplier (L56 guidance paragraph 220). Where the supply and the pipework were installed at different times, the person who finally connects them is responsible for testing and purging (paragraph 221).

If the test fails or you find a leak

L56 says a leak can be located by smell, by gas detectors approved for flammable atmospheres, by leak detection fluid, by pressure test equipment, or by a mix of these (guidance paragraph 122). Never use a flame or other source of ignition to look for one.

An installation that has failed its tightness test has not met regulation 22(1). Do not put it into use. Find and repair the leak, then test again.

If you cannot make it safe, the regulations and L56 say:

You must tell the responsible person for the premises, and the owner if different, that the appliance or installation is dangerous (regulation 34(3)). L56 says to do this in writing, and to say that it could cause death or serious injury and that using it is an offence (guidance paragraphs 286 and 291).
You have no legal power to disconnect without the responsible person's agreement. If they will not agree, label it as unsafe and, with their agreement, close the appliance shut-off device if one is fitted (guidance paragraph 287).
If they still will not agree to repair or disconnection, L56 recommends contacting the gas supplier for LPG, or 0800 111 999 for natural gas (guidance paragraph 288).
The responsible person must not use, or let anyone use, an appliance they know or suspect is dangerous (regulation 34(1)).

The industry's classification of unsafe situations, including the "Immediately Dangerous" and "At Risk" categories and the warning notices that go with them, is set out in the Gas Industry Unsafe Situations Procedure. L56 refers to it, but we could not read it from an openly published official source, so this page does not restate it. Use the current edition.

Landlord gas safety checks

A landlord safety check must include at least the matters in regulation 26(9): the flue, the combustion air supply, the operating pressure or heat input (or combustion performance where those cannot reasonably be checked), and safe operation (regulation 36(9)). The regulation does not list a tightness test by name. It says the check is not limited to those items.

L56 says a safety record should not be issued until all the required tests and examinations have been completed on every relevant appliance and flue (ACOP paragraph 302). The record must include any safety defect found and any remedial action taken (regulation 36(3)(c)).

What to record

The regulations do not prescribe a form for a tightness test result. The standard you test to may. Where a test forms part of a landlord safety check, the record must also carry the details regulation 36(3)(c) lists, including the date, the address, each appliance checked, any defect and action taken, and your name, signature and registration number.

CertBox has certificate templates for gas testing and purging, commissioning and landlord safety records, linked below.

Sources

Checked against these on 2026-09-30.

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Corrected and updated 2026-09-30. This article is for general guidance only and does not constitute legal or professional advice. Always refer to the relevant standards and consult qualified professionals for definitive requirements.

Gas tightness testing: what the law requires