A gas safety certificate, often called a CP12, is the document a Gas Safe registered engineer issues after inspecting the gas appliances and flues at a property. It records the date of the check, the appliances tested, and whether each one is safe to use. It is not a guarantee or a warranty — it is a snapshot of safety on the day of inspection.
The "CP12" name comes from the old paperwork code for a Landlord Gas Safety Record. The format has changed over the years, but the term has stuck and is still widely used to mean the same thing.
What a gas safety certificate records
The certificate is a written record of the inspection. It identifies the property, the engineer carrying out the work, and their Gas Safe Register number. It then lists each gas appliance and flue that was checked, along with the result for each.
Typical details captured on the document include:
- The address of the property inspected.
- The name, signature and Gas Safe licence number of the engineer.
- A description and location of each appliance — for example, a boiler in the kitchen or a gas fire in the lounge.
- Whether each appliance was tested, and if any could not be (for instance, if it was inaccessible).
- The safety check results, including any defects found.
- Any remedial action taken or recommended.
- The date of the inspection and the date the next one is due.
Where an appliance is found to be unsafe, the certificate should record this clearly. A dangerous appliance may be classed as "At Risk" or "Immediately Dangerous", and the engineer will usually note what action was agreed with the person responsible for the property.
Who legally needs one
A gas safety certificate, often called a CP12, is the document a Gas Safe registered engineer issues after inspecting the gas appliances and flues at a property.
The clearest legal duty falls on landlords. Under the Gas Safety (Installation and Use) Regulations 1998, a landlord must arrange an annual gas safety check on every gas appliance and flue they are responsible for in a rented property. This applies to most residential lettings, including houses, flats and rooms let within a shared house.
The landlord must keep a copy of the record and provide one to each tenant. A copy should go to existing tenants within 28 days of the check, and to any new tenant before they move in. Records are normally kept for at least two years.
The duty sits with the landlord even where a letting agent manages the property, though responsibility can be passed to the agent by written agreement. Either way, the law expects the check to be carried out by an engineer on the Gas Safe Register — the official body that licences gas engineers in the UK. Anyone working on gas appliances must be registered, and tenants can ask to see the engineer's identification.
Homeowners are not legally required to hold a gas safety certificate for their own home. There is no statutory annual check for an owner-occupier. That said, many people choose to have appliances inspected regularly, and a current safety record is often requested when selling a property or as part of an estate's paperwork. Some social housing providers and managing agents also set their own internal requirements.
Other situations where a check is commonly required include holiday lets, caravans and residential boats that are rented out, and certain commercial premises. The exact obligation depends on who controls the appliance and the tenancy arrangement.
What the inspection checks
The purpose of the inspection is to confirm that each gas appliance is working safely and that combustion gases are being removed properly. It is a safety check rather than a full service, though an engineer may carry out both during the same visit if asked.
A standard appliance inspection typically covers:
- That the appliance is fitted and operating correctly, and burning gas as it should.
- That the flue or chimney is removing combustion products safely to the outside.
- That the appliance has an adequate supply of air for safe burning, known as ventilation.
- That gas pressure and burner operation are within the correct range.
- That any safety devices on the appliance are functioning.
- A check for signs of incomplete combustion, which can produce carbon monoxide.
The engineer is checking the appliances and flues only — not the whole property. A safety check is narrower than a service: a service involves cleaning and inspecting internal components, while the safety check focuses on whether the appliance is safe to use. If a fault is found, the engineer will record it and, where the risk is serious, may disconnect or recommend not using the appliance until repairs are made.
Carbon monoxide is a particular concern because it is colourless and odourless. Although the safety check looks for warning signs, it does not replace a working carbon monoxide alarm, which is a separate requirement in many rented properties.
How long a certificate lasts
A gas safety certificate is valid for twelve months from the date of the check. For rented properties, the law requires a new inspection at least every year, so the record needs renewing before it expires.
To avoid gaps, the regulations allow the annual check to be carried out up to two months before the current certificate runs out, without shortening the new expiry date. In other words, an early check keeps the renewal date anchored to the original anniversary rather than pushing it forward. This makes it easier to keep checks on a consistent yearly cycle.
If a check is missed and the certificate lapses, the next inspection simply resets the twelve-month period from its own date. A lapsed record does not make the appliances unsafe on its own, but for a landlord it does mean a legal duty has not been met, which can carry penalties.
The certificate reflects the state of the appliances on the day of inspection. A fault can develop at any time, so a valid record should not be treated as a permanent assurance. Anyone who smells gas, notices a boiler behaving unusually, or hears a carbon monoxide alarm should act straight away rather than waiting for the next scheduled check.