What Happens During a Gas Safety Inspection (CP12)?
A step-by-step walkthrough of a landlord gas safety check, from arrival to certificate issue, so you and your tenants know exactly what to expect on the day.
By First Certify · 2026-09-14 · 6 min read
First Certify is a UK property compliance platform staffed by accredited assessors and qualified engineers. This article has been reviewed for accuracy against current UK regulations, including MEES, the Electrical Safety Standards 2020, and the Gas Safety (Installation and Use) Regulations 1998.
A gas safety inspection, also known as a CP12, is one of the shortest and most straightforward compliance visits a landlord needs to arrange. The entire check typically takes 30 to 45 minutes, and the digital certificate is sent to your inbox within 72 working hours — most within 24 to 48. But because it involves gas appliances, many landlords and tenants are unsure what actually happens during the visit. This article walks through the process step by step.
Before the engineer arrives, make sure they can access the boiler, the gas meter, and any other gas appliances in the property, such as a hob, fire, or water heater. If the property is tenanted, give your tenant at least 24 hours notice as per your tenancy agreement. The engineer will need to turn appliances on and off during testing, so it helps if someone is present to provide access.
When the engineer arrives, they will show their Gas Safe Register ID card. This is worth checking, as only engineers on the Gas Safe Register are legally permitted to carry out gas safety checks and issue a CP12. Every engineer on the First Certify platform is Gas Safe registered, but it is still good practice to verify.
The inspection begins at the meter. The engineer checks the meter installation, the gas pipework leading from it, and the emergency control valve. They carry out a gas tightness test, which involves pressurising the pipework and monitoring for any pressure drop that would indicate a leak. This is one of the most important parts of the check, as an undetected gas leak is a serious safety hazard.
Next, the engineer inspects each gas appliance in turn. For the boiler, this includes checking the flue is correctly installed and terminates safely outside, verifying that the boiler is burning gas efficiently, and testing the safety devices such as the flame failure device and overheat thermostat. The engineer will fire the boiler and may use a flue gas analyser to measure carbon monoxide and carbon dioxide levels in the flue gases, confirming the appliance is operating within safe limits.
If the property has a gas hob, the engineer checks the burners for stable flames, adequate combustion, and that the gas supply is secure. For a gas fire, they inspect the flue or chimney, check the ventilation, and verify that the appliance is safely secured. Any other gas appliances, such as water heaters or warm air heaters, are checked in the same way.
Throughout the inspection, the engineer looks for any signs of deterioration, damage, or non-compliance. This includes checking that appliances have adequate ventilation, that flues are not blocked or restricted, and that safety devices are functioning. If an appliance fails any part of the check, the engineer will flag it on the certificate and, in the case of an immediate danger, may disconnect the appliance and issue a warning notice.
Once all appliances have been checked, the engineer completes the CP12 certificate. This documents the date of the inspection, the engineer details, the appliances checked, and the results. If everything passes, the engineer records the results on the CP12 certificate. A digital copy is sent to your inbox within 72 working hours — most within 24 to 48 — and you must provide a copy to your tenants within 28 days of the check.
If any appliances fail, the certificate will note the reason and the engineer will advise on the necessary remedial work. A failed appliance does not necessarily mean the entire certificate is invalid, but any immediately dangerous appliance must be made safe before the property can continue to be let. The engineer will explain the next steps clearly.
After the visit, you must provide a copy of the CP12 to your tenants within 28 days, and to any new tenant before they move in. You must retain records for a minimum of two years. At First Certify, we store your certificate digitally and send automated reminders when your next annual check is due, so you never risk a gap in compliance.
FAQs
How long does a gas safety inspection take?
A standard CP12 inspection takes 30 to 45 minutes for a property with a boiler and a couple of gas appliances. The engineer needs access to all gas appliances and the meter. The digital certificate is sent to your inbox within 72 working hours — most within 24 to 48.
Do I need to be present during the gas safety check?
Someone must be present to provide access to the boiler, meter, and any gas appliances. If the property is tenanted, your tenant can provide access. Give at least 24 hours notice as per your tenancy agreement.
What happens if an appliance fails the gas safety check?
If an appliance is flagged as immediately dangerous, the engineer may disconnect it and issue a warning notice. The certificate will note the failure and the engineer will advise on remedial work needed. Any immediately dangerous appliance must be made safe before the property can continue to be let.