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.
Gas Safety Certificate: What Do They Check?
During a gas safety inspection, engineers examine several key areas to ensure everything is safe and working as it should.
Gas appliances
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.
Gas pipework
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.
Flues and chimneys
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.
Ventilation
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.
Appliances
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.
What Happens During the Inspection Process?
Here’s a typical workflow for a gas safety inspection:
- Initial visual checks of appliances, pipework, and ventilation.
- Tightness test for gas leaks.
- Test and measure each appliance for safe operation.
- Use of flue gas analyser (for boilers/fires) to assess emissions.
- Record findings on the Gas Safety Certificate.
- Advise landlord or tenant of any defects and actions taken.
- 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.
What a Valid Gas Safety Certificate Includes
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.
Don’t Forget
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 which home-energy grants you might be eligible for.
People Also Ask
A Gas Safe engineer inspects all gas appliances, pipework, and flues for safe operation. They test for leaks, check ventilation and safety devices, and ensure appliances are stable and efficient.
Yes, radiators are inspected as part of the heating system connected to the boiler. The engineer checks that the system is safe, with no leaks or carbon monoxide risks.
If a check fails, the certificate will mark appliances as “Not Safe to Use.” It will also list failure codes and details explaining why.
A typical gas safety check lasts between 30 and 60 minutes, depending on the number of appliances.
A gas safety check covers all gas appliances, including the boiler, but it’s not the same as a full boiler service. A service involves a deeper inspection and cleaning, while the certificate confirms legal safety compliance.
Yes, only Gas Safe registered engineers can legally install or repair boilers. DIY gas work is dangerous and can lead to prosecution and heavy fines.
The law doesn’t give an exact time limit, but heating and hot water must be restored within a “reasonable” period. In winter, issues should typically be fixed within 24 hours.
Yes, installing new back boilers has been banned since 2005 due to efficiency and safety concerns. Existing ones can still be used, but they are costly to run and difficult to repair.
Landlords must have all gas appliances, including boilers, checked at least once every 12 months. This is a legal requirement for tenant safety.
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