What Is a Gas Tightness Test and When Do Landlords Need One?

What is a gas tightness test and why might a landlord need one?

A gas tightness test checks whether gas pipework is safe and leak-free. A qualified engineer carries out the procedure to confirm the pipework holds pressure properly. Landlords may need one if gas systems are installed, altered, or suspected of leaking. It is a key part of gas pipework testing and helps maintain system safety.

What Is a Gas Tightness Test?

A gas tightness test confirms that the gas pipework in a building is sealed and not leaking. It involves isolating the gas supply and applying a set pressure to the system. If the pressure remains stable, the pipework is considered safe.

The test is carried out by a Gas Safe registered engineer using a manometer. The engineer closes the Emergency Control Valve (ECV), seals the system (also known as system isolation), and measures whether any pressure drops over a set period. Even a small drop can indicate a leak.

This test is not part of standard appliance checks. It is specifically for the installation pipework and supports safety standards set by the Gas Safety (Installation and Use) Regulations 1998. It forms an essential part of pipework integrity checks and proactive leak detection.

What Does a Gas Tightness Test Check and Why Does It Matter?

This test focuses on the gas installation pipework from the meter to the appliances. It checks that the system holds pressure without any drop. If pressure falls, it suggests a potential leak in the pipework.

The engineer uses a manometer to measure standing pressure and monitor it over time. A steady reading indicates the system passes. Any drop means further checks are needed.

Leaks can happen in hidden or hard-to-reach areas. They may not produce obvious signs like smells or noise. This is why gas leak testing is vital. It identifies faults early and helps ensure safe operation.

By confirming pipework integrity, the test supports leak prevention and overall system safety. It helps identify problems that might go unnoticed during appliance checks and confirms pressure stability in older or altered systems.

Gas Tightness Test vs Gas Safety Certificate: What’s the Difference?

A gas safety certificate, also known as a CP12 or Gas Safety Record, confirms that gas appliances work correctly and that pipework appears safe from a visual inspection. It does not include pressure testing unless specifically required.

A gas tightness test is a different process. The engineer seals the system and applies pressure to check for leaks. This test does not replace a CP12 and is not part of the standard annual check unless necessary.

Some landlords believe their pipework has been fully tested just because they have a certificate. That is not always true. Understanding the difference between appliance testing and pipework assessment helps landlords avoid compliance gaps and stay informed.

When Do Landlords Need a Gas Tightness Test?

These are the most common times when a gas tightness test is required:

1. New installations – Testing is done before pipework is used to confirm safety.
2. Repairs or changes – Any alterations or repairs to the pipework need testing to ensure no leaks were introduced.
3. System recommissioning – Systems that have been unused for a while should be tested to confirm they still hold pressure.
4. Suspected leaks – If a leak is suspected, a tightness test can help identify the issue quickly and confirm the need for gas pipework repairs.

In these situations, testing is essential to keep systems safe and working properly. These fall under formal gas tightness test requirements outlined by installation standards.

When Is a Gas Tightness Test Recommended but Not Mandatory?

There are other situations where testing is not legally required but still wise:

• Old systems – Over time, joints and materials can wear down, making preventative safety checks useful.

• Long periods without testing – A system left unchecked might have hidden faults or slow leaks.

• New tenants – Testing before a new tenancy begins adds confidence and creates a clean compliance record.

• Planned maintenance – Some landlords include tightness testing in their landlord gas safety best practice routines.

While not mandatory, these checks support risk management and demonstrate due diligence.

Why Gas Tightness Testing Is Especially Relevant for London Landlords

Many London homes are older or split into flats, which often means more complex gas systems and shared services. This increases the importance of gas tightness testing.

Gas pipework in HMOs or conversions may run through basements, risers, or communal areas. These are difficult to inspect and can hide faults. Pressure testing provides a more complete picture of system condition, especially where legacy infrastructure is involved.

In densely populated areas, a leak could affect more than one household. Proactive testing supports London landlord gas safety and helps limit broader risks.

What the Results Mean for Landlords (Pass, Fail, or Further Work)

The results of a gas tightness test fall into three categories:

• Pass – The system holds pressure and is safe to use.

• Fail – There is a pressure drop, which points to a likely leak and the need for remedial action.

• Further investigation – The test results are unclear, and more checks are needed to verify pipework condition.

A failed test does not always mean major work. Small leaks are common and often easy to fix. The engineer will explain what is needed and whether re-testing is required. Clear documentation of findings helps maintain compliance records.

By understanding the outcomes, landlords can make sensible decisions and protect both tenants and property.

Common Gas Tightness Test Questions Landlords Ask

How much does a gas tightness test cost?
It usually costs between £60 and £100, depending on the property and access to the system. This is the standard range for a typical gas tightness test cost.

Will it disrupt tenants?
The test involves briefly turning off the gas, but it is quick and tidy.

How long does the test take?
Most properties take between 30 and 60 minutes to complete the test. That is how long a gas tightness test takes in most residential settings.

Do tenants need to be there?
Only if the gas meter or ECV is inside their flat. If not, the engineer can carry out the work without them.

What documents will I get?
The engineer can provide a written report or include the results in the service notes. It is not a formal certificate but helps build a safety record and supports future compliance documentation.

Who can carry out the test?
Only a Gas Safe registered engineer is qualified to do this work. Their registration confirms they are trained and authorised to carry out pressure testing and follow installation standards properly.