What Does a Gas Safety Certificate Check?

A Gas Safety Certificate (often referred to as a CP12) confirms that gas appliances, flues, and pipework in a property are safe to use. This guide breaks down the specific components engineers inspect during the process, so you know exactly what’s being checked and why it matters.

During a gas safety inspection, engineers examine several key areas to ensure everything is safe and working as it should.

They begin with gas appliances, including boilers (whether combi or system), gas fires, cookers, hobs, and any other gas appliances supplied by the landlord. Each appliance is tested for operating pressure and gas rate, burner pressure or heat input, the condition of its casing and components, and the proper operation of built-in safety devices. Where relevant, engineers will also check the flame picture to confirm it is burning correctly.

Next comes the gas pipework. A tightness test is carried out to detect any leaks, and engineers also carry out a visual inspection of accessible pipework to spot signs of corrosion, wear, or damage.

The inspection also covers flues and chimneys. Their condition and positioning are checked, along with ensuring that exhaust gases can safely discharge without obstruction. If accessible, chimneys are visually inspected, and flue gas analysers are used to assess both safety and efficiency.

Proper ventilation is another essential part of the process. Each appliance must have the right airflow and room size to operate safely, and engineers will confirm that these requirements are met.

Where carbon monoxide alarms are required, engineers make sure they are fitted in the correct place and working properly, especially in areas considered high risk.

Finally, engineers assess the overall condition of every appliance. Each one is classified as either Safe, At Risk (AR), or Immediately Dangerous (ID). If an appliance is found to be unsafe, it may be disconnected on the spot to protect occupants.

Here’s a typical workflow for a gas safety inspection:

1. Initial visual checks of appliances, pipework, and ventilation.
2. Tightness test for gas leaks.
3. Test and measure each appliance for safe operation.
4. Use of flue gas analyser (for boilers/fires) to assess emissions.
5. Record findings on the Gas Safety Certificate.
6. Advise landlord or tenant of any defects and actions taken.
7. Issue certificate if all appliances meet safety standards.

The process usually takes between 30 minutes to 1 hour, depending on the number and type of appliances.

After the inspection, the certificate will document:

• Address of the property.
• Date of inspection.
• Engineer’s name and Gas Safe registration number.
• Description and results of all appliance checks.
• Any identified defects and actions taken.
• Signature of the engineer.
• Next inspection due date.

Understanding what is checked during a gas safety certificate gives peace of mind, whether you’re a landlord staying compliant or a tenant ensuring a safe living environment.

The checks aren’t just box-ticking exercises, they’re vital safety steps that prevent gas leaks, carbon monoxide exposure, and fire risks.

If you’re unsure about the condition of your gas systems, don’t wait for the annual inspection. Book a registered engineer and stay ahead of any issues.

Use our EPC checker to see how energy efficient your home is, and/or order a new EPC.

Knowing your EPC can help you understand what support you might be eligible for under ECO4, a government scheme that provides free or discounted home energy upgrades for low-income households, and the Great British Insulation Scheme, which offers funding towards insulation to help cut energy bills.