CP12 Gas Safety Certificate: Costs & What's Included
The CP12 gas safety certificate is one of the simplest but most important parts of a landlord’s legal duties. This guide explains what a CP12 includes, how much a gas safety check costs, and what a Gas Safe engineer actually does during the inspection.
Why Do Landlords Need a CP12 Certificate?
If you're a landlord in the UK, the CP12 gas safety certificate is one of the most important legal documents you’ll deal with each year – it proves your gas appliances are safe and keeps you on the right side of the law. But many landlords still aren’t entirely sure what a CP12 includes, how much it should cost, or what the engineer is actually checking.
This short guide explains everything you need to know in plain English, including typical costs (2025) and a step-by-step breakdown of the inspection.
For a wider view of fines, grace periods and eviction rules, see our main guide: Gas Safety Certificates: Fines, Grace Periods, Section 21 and CP12 Explained.
What Is a CP12 Gas Safety Certificate?
A CP12 is the official record confirming that a qualified Gas Safe registered engineer has inspected the gas appliances, flues and pipework in your rental property and confirmed they are safe on the day of the inspection.
A valid CP12 typically includes:
- Engineer’s name and Gas Safe registration number
- Property address
- Date of the check
- All appliances tested (boiler, hob, gas fire, water heater, etc.)
- Results of safety checks
- Any defects or advisory notes
- Classification of issues (“At Risk”, “Immediately Dangerous”, etc.)
- Confirmation that appliances are safe
- The next check due date
Landlord responsibilities for gas safety are set out in the official HSE guidance for landlords , which requires annual checks by a Gas Safe registered engineer.
How long is a CP12 valid?
A CP12 certificate lasts 12 months. There is no grace period after expiry — once it lapses, you are legally out of compliance.
If you’re unsure what happens when a certificate expires, read our guide on Gas Safety Certificate “Grace Periods” for a full breakdown of the rules.
How Much Does a Gas Safety Check Cost?
Prices vary depending on location, appliance count, and whether you combine the check with a boiler service. Across the UK, you can expect:
£60–£120 for a standard check on a single boiler (most landlords will fall in this range).
Typical appliance add-ons:
- + £15–£25 for a gas hob
- + £20–£35 for a gas fire
- + £20–£30 for a second boiler or heater
If you combine the gas safety check with a boiler service, £110–£160 is the normal range (with London at the higher end).
External cost guides also suggest that a typical domestic gas safety certificate falls in the £60–£90 range for a standard property, with extra fees for additional appliances.
Why extremely cheap CP12s (£35–£45) are risky
A compliant inspection takes time. Ultra-cheap certificates often indicate:
- Rushed checks
- Incomplete testing
- No flue analysis
- Poor documentation
These certificates may not protect you if there is an investigation after an incident.
If you’re wondering what happens when a certificate is missing or invalid, our guide Gas Safety Fines explains the penalties councils and HSE can issue for non-compliance.
What Actually Happens During a Gas Safety Check? (Step-by-Step)
During a proper CP12 inspection, a Gas Safe engineer follows a structured process to confirm that all appliances and pipework are safe. The Gas Safe Register also sets out what a thorough gas safety check should include.
1. Visual inspection of all gas appliances
The engineer checks the general condition of each appliance, looking for unsafe modifications, signs of leaks, correct installation and adequate ventilation. This includes boilers, hobs, gas fires and water heaters.
2. Flue and chimney checks
The flue and chimney are inspected for integrity, routing, termination, blockages, cracks and any signs of spillage. Unsafe flues are a significant carbon monoxide risk.
3. Pressure and tightness testing
The engineer tests the gas pipes for correct pressure, leaks and consistent flow, often by turning off appliances and using a calibrated pressure gauge.
4. Burner and flame analysis
Burner pressure, flame colour and shape, combustion performance and safety devices are checked. More complex boilers may also require flue gas analysis.
5. Appliance safety controls
Built-in safety devices such as flame-failure devices, overheat stats, thermocouples, interlocks and cut-offs are tested to make sure they operate correctly.
6. Carbon monoxide and ventilation assessment
Ventilation levels are checked and the engineer looks for any signs of carbon monoxide spillage or unsafe room layout. CO alarms may also be checked and advisory notes given.
7. Identifying and classifying defects
If problems are found, they are classified as:
- Not to Current Standards (NCS) – still safe to use, but advisory notes are given.
- At Risk (AR) – unsafe if conditions worsen; the appliance should not be used until fixed.
- Immediately Dangerous (ID) – appliance must be turned off and isolated immediately.
A landlord cannot override an “ID” classification.
8. Recording all results and issuing the CP12
After testing, the engineer records appliance readings, defects, work completed, safety outcomes and the expiry date, then issues the CP12 — usually as a digital PDF.
How Long Does a Gas Safety Check Take?
Most checks take 30–60 minutes for a single boiler, and 60+ minutes if multiple appliances are present. It will take longer if defects are found or appliances are difficult to access.
If an engineer is “in and out in 10 minutes”, the inspection was not thorough and may not stand up to scrutiny if something goes wrong.
What Does a CP12 Not Include?
A CP12 is not a boiler service.
It does not include:
- Deep cleaning of components
- Replacement of seals
- Removal of combustion chamber covers
- Internal inspection of heat exchangers
- Detailed system health checks
A gas safety check ensures appliances are safe, not maintained. For best practice, many landlords book CP12 and boiler servicing together.
How to Prepare for a Smooth Gas Safety Check
- ✔ Ensure easy access to the boiler
- ✔ Clear access to gas fires or hobs
- ✔ Make sure tenants are aware of the appointment
- ✔ Provide engineer access instructions (keys, codes, concierge, etc.)
- ✔ Keep previous CP12s on file
Summary: The CP12 Is a Simple but Crucial Part of Your Legal Duties
A CP12 certificate is a landlord’s yearly confirmation that every gas appliance is safe. The check is inexpensive, quick and straightforward — but skipping it or allowing it to expire carries serious risk.
- A proper check takes 30–60 minutes
- A CP12 lasts 12 months
- There is no grace period after expiry
- Always provide the certificate to your tenant
- Keep digital copies and maintain a continuous chain of records
With good organisation and a trusted Gas Safe engineer, gas safety compliance becomes one of the simplest parts of managing a rental property.
For related guidance, you may also find these useful:
• Gas Safety Certificate Grace Periods: The Truth Landlords Need to Know
• Gas Safety Fines: Penalties for Missing or Expired CP12s
• Can I Evict a Tenant Without a Gas Safety Certificate?
Important: This article is for general information only and is not legal advice.
Always seek independent legal advice or consult a specialist with regards to any legal matters regarding gas safety.
Information accurate as of December 2025.
