CP12 Gas Safety Certificate UK 2026: Complete Guide for Gas Engineers and Landlords

What is a CP12 gas safety record?

A CP12 is the informal but widely used name for the Gas Safety Record — the official document that a Gas Safe registered engineer must complete after carrying out a gas safety inspection at a residential rental property. The official term under the Gas Safety (Installation and Use) Regulations 1998 is "gas safety record," but the CP12 label has stuck in industry usage for decades.

The name derives from the form number used by CORGI — the Council for Registered Gas Installers — which was the UK's gas registration body before it was replaced by the Gas Safe Register in 2009. CORGI's inspection form was numbered CP12, and the shorthand carried over when Gas Safe took over the registration scheme. Today the form itself has no fixed number; different software platforms and engineering firms produce their own versions, but the document must contain the same prescribed fields regardless of its appearance.

A CP12 certifies that a qualified engineer has inspected the gas appliances and flues at a property, checked that they are operating safely and within the manufacturer's parameters, and confirmed that there are no immediate gas safety hazards. It is not a service record — a gas safety check and a boiler service are separate jobs, though they can be carried out on the same visit. The safety check focuses on whether each appliance is safe to use; the service involves cleaning, adjusting, and maintaining the appliance to keep it running efficiently.

What the Gas Safety Regulations 1998 require

The Gas Safety (Installation and Use) Regulations 1998 place a legal duty on landlords of residential properties to ensure that all gas appliances, fittings, and flues provided for tenants are maintained in a safe condition. The key obligation is to arrange a gas safety check every 12 months, carried out by a Gas Safe registered engineer.

The duty covers all gas appliances and flues that the landlord provides or is responsible for maintaining. This includes boilers, gas cookers, gas fires, and any other gas-burning appliance that forms part of the let. It does not cover appliances owned by the tenant themselves, though the engineer must still check the flue associated with any such appliance if it passes through a communal area.

On completion of the check, the engineer issues the gas safety record. Landlords must give a copy of the current gas safety record to existing tenants within 28 days of the check being completed. New tenants must receive a copy before they move in. Landlords are required to keep records of all gas safety checks for a minimum of two years.

There is no grace period or exemption. Even if an appliance is rarely used or a property has been empty, the annual obligation still applies while the property is let. Failure to comply is a criminal offence under the Health and Safety at Work etc. Act 1974 and can result in enforcement action by the Health and Safety Executive (HSE).

What a Gas Safe engineer checks during a CP12 inspection

A gas safety check is a methodical series of tests and visual inspections carried out on each appliance and its associated pipework, controls, and flue. Here is what a competent engineer checks.

Appliance safety checks

• Working pressure: The engineer verifies that the gas pressure at the appliance is within the manufacturer's specified range. Incorrect working pressure can cause incomplete combustion, producing carbon monoxide.
• Heat input: The gas rate (volume consumed per hour) is measured and compared against the appliance data plate to confirm the burner is operating at the correct heat input.
• Operating pressure: Where accessible, the engineer checks that the burner pressure corresponds to manufacturer specifications for the given heat setting.
• Safety devices: Thermostats, overheat cut-outs, flame failure devices, and pressure relief valves are tested to confirm they operate correctly and would shut the appliance down if a fault developed.
• Combustion analysis: For boilers, the engineer typically takes a flue gas analysis reading to check CO/CO₂ ratios, confirming complete combustion is occurring and carbon monoxide is not being produced at dangerous levels.

Flue and ventilation checks

• Flue integrity and spillage: For open-flued appliances (those that draw combustion air from the room), the engineer carries out a spillage test to confirm that combustion gases are being safely discharged up the flue rather than spilling back into the room.
• Flue condition and termination: The visible sections of flue and the terminal position are inspected for signs of damage, blockage, or incorrect positioning that could allow exhaust gases to re-enter the building.
• Ventilation: Rooms containing open-flued appliances must have adequate permanent ventilation. The engineer checks that any required air bricks or purpose-provided vents are present, unobstructed, and correctly sized.

Emergency controls and visual checks

• Emergency control valve: The location and operability of the emergency control valve (the main gas isolator, usually near the meter) is confirmed and noted on the record.
• Visual check of pipework and connections: Accessible gas pipework, flexible connectors, and appliance connections are visually inspected for signs of corrosion, damage, or improper installation.

What must appear on a CP12 certificate

The Gas Safety (Installation and Use) Regulations 1998 specify the information that must be included on every gas safety record. A document that omits any of these fields is not a valid gas safety record and does not satisfy the landlord's legal obligation.

Many gas safety records also include a next inspection due date, the landlord's name and address, and test readings for each appliance — these are best practice rather than a strict legal requirement, but they help demonstrate that a thorough check was carried out.

CP12 renewal: the 2-month early renewal window

Landlords who arrange their CP12 renewal up to two months before the current certificate's expiry date do not lose the remaining time on the existing certificate. The new certificate's 12-month validity is calculated from the original expiry date, not from the date the new check was carried out. This is one of the most useful and underused provisions in gas safety compliance.

Without this rule, a landlord who renewed two months early would lose two months of coverage every cycle, meaning they would need to book more frequently over time to stay compliant. The two-month window is designed to prevent that drift and to make it practical for landlords to book checks in advance without being penalised.

If the check is carried out more than two months before the expiry date, the two-month rule does not apply. In that case, the new certificate runs for 12 months from the date of the inspection. For a landlord booking very early — say, four months before expiry — that means losing roughly two months of validity compared to booking within the window.

How much does a CP12 check cost in the UK?

CP12 check prices vary depending on the number of gas appliances at the property, the region, and whether the engineer is combining the safety check with a boiler service or other gas work. The table below shows typical costs for a standalone gas safety check in 2026.

Many engineers offer a reduced combined price when the gas safety check and annual boiler service are booked together, as it saves a separate call-out. For landlords with multiple properties, asking about a block rate for same-day or same-week checks across several addresses can reduce the per-property cost meaningfully.

Landlord obligations: what happens if you miss the annual check

Failing to carry out the annual gas safety check is a criminal offence under the Health and Safety at Work etc. Act 1974. The Health and Safety Executive is the enforcing authority for the Gas Safety Regulations, and it takes non-compliance seriously, particularly where tenant safety is at risk.

The annual cost of a CP12 check — typically £60–£120 — is modest compared to the potential consequences of non-compliance. Treating it as a fixed cost of letting and booking it into a calendar reminder well before the current certificate expires is the simplest way to avoid any risk.

Related guides

If you found this guide useful, the following pages cover related topics for gas engineers and landlords.

• →Gas engineer hourly rate UK 2026 — day rates, call-out charges, and regional pricing for gas engineers across the UK.
• →Gas Safe registration — how to apply, what qualifications you need, renewal costs, and what the Gas Safe Register covers.