What a CP12 Actually Is and Why the Paperwork Matters
A CP12 is the Landlord Gas Safety Record. The name comes from the old Gas Safety Check form coding, and while CORGI no longer exists, the name stuck. Under Regulation 36 of the Gas Safety (Installation and Use) Regulations 1998, a landlord who lets a property containing gas appliances must arrange an annual gas safety check carried out by a Gas Safe registered engineer. You must issue the completed record to the existing tenant within 28 days of the check, and to any new tenant before they move in. Landlords must keep a copy for at least two years.
The legal weight of the document sits on you, not the landlord. If the certificate is incomplete, contains errors, or was signed by someone not Gas Safe registered for the appliance categories in question, you are the person exposed. The Health and Safety at Work etc. Act 1974 underpins the broader duty of care, but Regulation 36 is the specific provision that creates the obligation, sets the 28-day issue deadline, and defines what the record must contain.
There is no prescribed layout for a CP12 under the regulations. What is prescribed is the data it must contain. Any printed or digital format that captures all mandatory fields satisfies the legal requirement. That said, deviating from the widely recognised format creates confusion and occasionally triggers unnecessary landlord complaints, so most engineers stick to the standard layout.
What You Need Before You Start Filling Out the Form
Getting to the end of a job and realising you are missing the boiler serial number, or that you did not record the flue CO reading, means going back on site or issuing a certificate with gaps. Neither is acceptable. Prepare the following before you put pen to paper or tap into a digital form.
You will need your Gas Safe registration number and the licence card number relevant to the appliance categories you are certifying. You will need the full property address, the landlord's name and address, and the tenant's name if one is in occupation. On the appliance side, you need the make, model, and serial number for every appliance included in the check, the location of each appliance, the type of flue, and the ventilation provision.
You will also need your test results to hand before you start completing the results section. That means flue gas analysis readings, pressure readings, operating pressure at the appliance, gas rate where checked, and the results of any visual inspections of the installation pipework. Do not try to fill in results from memory at the end of the day. Record them on your job notes on site, then transfer them to the certificate.
- •Gas Safe registration number and relevant appliance categories
- •Full property address and landlord contact details
- •Tenant name (if applicable)
- •Make, model, and serial number for each appliance
- •Flue type and condition notes
- •Ventilation type and condition
- •Flue gas analysis results (CO and CO2 readings)
- •Inlet and operating pressures
- •Gas rate (if checked)
- •Visual inspection findings for pipework and meters
Step 1: Complete the Property and Landlord Details
Start at the top of the form. Write the full property address including postcode. Do not abbreviate. If the certificate ever needs to be referenced in a dispute or enforcement action, a partial address creates an immediate problem. Enter the landlord's name and address. If the landlord is a company, use the registered company name, not a trading name or the name of the person who called you.
Enter the date of the inspection. This date triggers the 28-day clock for issuing the record to the tenant under Regulation 36(3)(b). If you complete the check on 3 June, the record must reach the existing tenant by 1 July. The next annual check is due by 3 June the following year. Some engineers write the due date on the certificate for the landlord's benefit; this is not mandatory but is good practice.
Common pitfall: entering the date you write up the certificate rather than the date you carried out the inspection. If you did the check on a Tuesday and completed the paperwork on Thursday, the inspection date is Tuesday. HSE has used discrepancies between gas meter data logs and certificate dates as evidence in prosecutions.
Step 2: Record Your Gas Safe Registration Details
This section establishes your competence and legal authority to issue the certificate. Enter your full name as it appears on your Gas Safe registration, your Gas Safe registration number, and the appliance categories you are registered for. If you are certifying a boiler and a gas hob, you need to be registered for both. Issuing a certificate for an appliance outside your registration categories is a criminal offence.
Some forms ask for your employer's details as well. As a sole trader, you are the employer and the employee, so enter your own business name. Do not leave this blank. HSE inspectors checking certificates will cross-reference the registration number against the Gas Safe Register. If your business name on the certificate does not match what is on the register, expect a call.
Common pitfall: using an old registration number after renewal, or copying the wrong number from a previous certificate. Check your current Gas Safe licence card rather than relying on a saved template. Registration numbers do not change, but categories can if you have lapsed and re-registered.
Step 3: List Every Appliance Checked
Each appliance checked must have its own row or section on the certificate. The mandatory information for each appliance is: location (e.g. kitchen, airing cupboard, garage), type of appliance (boiler, gas fire, cooker, etc.), make, model, and serial number. Do not group appliances. If there are four appliances, there are four entries.
The serial number is the field most commonly left blank or approximated. It matters because it is the unique identifier for the specific unit. In the event of an appliance recall, an insurance claim, or an HSE investigation, a certificate that says 'Ideal Logic Combi 30' without a serial number is significantly less useful than one with the full serial. Locate the data plate. On most boilers it is on the inside of the front panel. Photograph it on site.
Common pitfall: certifying appliances that are not within the property boundary or that belong to a tenant rather than the landlord. You are certifying the landlord's installation. If a tenant has brought in their own freestanding gas cooker, you should note it on your job record and advise the landlord in writing, but it should not appear on the CP12 unless the landlord has agreed to include it.
Step 4: Record Flue Flow, Ventilation, and Safety Device Results
For each appliance, the certificate requires you to confirm the flue type, record whether the flue flow test was satisfactory, note the ventilation provision (natural or mechanical, and whether it was adequate), and confirm the operation of safety devices. Work through each appliance in sequence rather than recording all flue results first and all ventilation results second. Going row by row reduces the chance of transposing results between appliances.
The flue flow test result is typically recorded as satisfactory or unsatisfactory, but your job notes should contain the actual readings. If a record is later challenged, 'satisfactory' on the certificate backed up by specific readings in your notes is a defensible position. 'Satisfactory' alone, with nothing to support it, is not.
Common pitfall: recording a safety device as 'not tested' when it should have been tested. If a safety device cannot be tested because of access, age, or condition, this should be recorded as a defect and classified appropriately under the 'At Risk' or 'Immediately Dangerous' categories. Leaving safety device fields blank is not the same as recording a tested and satisfactory result.
Step 5: Enter Gas Pressure and Combustion Analysis Readings
Record the operating pressure and, where applicable, the standing pressure for each appliance. These should match your on-site meter readings exactly. Do not estimate or round figures. Enter the actual figure from your manometer. Operating pressure for a natural gas appliance should typically be 20 mbar at the appliance; if your reading differs, investigate before issuing the certificate.
For the combustion analysis section, record the CO and CO2 readings taken at each appliance during operation. Also record the CO to CO2 ratio (CO/CO2 ratio). The relevant benchmark for boilers is typically a CO/CO2 ratio below 0.004 for a sealed flue appliance, in line with IGEM guidance. If readings exceed acceptable thresholds, the appliance cannot receive a satisfactory classification. Record what you found accurately, classify the situation correctly, and follow the correct notification procedure.
Common pitfall: recording combustion analysis readings taken during the first few minutes of appliance operation before it has reached steady state. Allow the appliance to run for a minimum of five minutes before taking the reading used on the certificate. Engineers in a hurry frequently record readings taken too early, which may not represent the appliance's actual performance.
Step 6: Classify Each Appliance and Installation
Every appliance must be classified as one of three things: safe to use (no defects found), At Risk (a defect is present but the appliance is not in immediate danger of causing injury if used with caution), or Immediately Dangerous (the appliance must be taken out of use straight away). This is not a box to fill in as a formality. It is the core safety judgement that gives the certificate its legal standing.
If you classify an appliance as At Risk or Immediately Dangerous, you must record the specific defect, advise the landlord or tenant in writing, and obtain a signature confirming they have been warned. For an Immediately Dangerous appliance, you should disconnect it or seal it off if you have authority to do so, or if the landlord or tenant refuses to let you disconnect it, note that refusal in writing on the certificate and in a separate letter. You are not personally liable for leaving a dangerous appliance connected if you have done everything within your power to warn the responsible party and have documented that warning.
Common pitfall: classifying an appliance as 'safe' when one or more test results are borderline. If your combustion analysis readings are within tolerance but only just, and the appliance is five years past its last service, the correct answer is probably 'At Risk' with an advisory. An over-generous classification that is later contradicted by a CO incident will be traced back to this certificate.
Step 7: Complete the Pipework and Meter Installation Section
The CP12 requires a visual inspection and, in most cases, a gas tightness test of the installation pipework. Record the result of your visual inspection of the pipework, noting any areas of corrosion, inadequate support, or proximity to electrical cables or heat sources. Record the result of the gas tightness test as satisfactory or unsatisfactory.
From 1 October 2026, IGEM/UP/1B Edition 4 changes how gas tightness testing permissible pressure drop is determined. Under Edition 4, the permitted pressure drop is calculated by reference to the Installation Volume of the pipework rather than the meter size. This is a significant methodological change. If you are completing a CP12 after that date, you must apply the Edition 4 methodology. Any perceptible movement on a U6 or E6 meter gauge during a tightness test will no longer be attributable to the installation pipework alone; it must be investigated. Check your training provider's updated guidance before October 2026 if you have not already done so.
Common pitfall: skipping the gas tightness test on a 'straight-forward' annual check because no work was carried out on the pipework. The Gas Safety (Installation and Use) Regulations 1998 require the installation to be checked for soundness as part of the annual inspection. The tightness test is not optional.
Step 8: Sign, Issue, and File the Certificate
Sign the completed certificate. Your signature confirms that the inspection was carried out in accordance with the Gas Safety (Installation and Use) Regulations 1998 and that the information recorded is accurate to the best of your knowledge. Do not sign a blank or partially complete certificate and fill it in later. Do not allow anyone else to sign a certificate in your name.
Under Regulation 36(3)(b), the record must be issued to the existing tenant within 28 days of the inspection date. Issue it by email with a read receipt, by post with proof of postage, or hand it over and get a signature. Keep a copy for your own records. As a sole trader, your business records are your professional defence. A certificate in your files that matches what was issued to the landlord and tenant is evidence that you did the job correctly.
Common pitfall: issuing the certificate only to the landlord and assuming they will pass it on to the tenant. That is the landlord's legal obligation, but HSE has in the past pursued engineers where there is evidence they knew the tenant was not receiving records. Your safest position is to issue directly to the tenant wherever possible and confirm you have done so in writing to the landlord.
- •Sign only when all fields are complete
- •Issue to the existing tenant within 28 days (Regulation 36(3)(b))
- •Issue to any new tenant before they move in
- •Landlord must retain a copy for at least two years
- •Keep your own copy indefinitely where possible
- •Send by email with read receipt or post with proof of postage
Worked Example: A Completed CP12 for 14 Birchwood Avenue
The following example shows how a correctly completed CP12 should look for a typical single-appliance let. Property: 14 Birchwood Avenue, Leeds, LS7 4RN. Landlord: Mr D. Patel, 22 Grange Road, Leeds, LS6 2TW. Tenant: Ms A. Harrison. Inspection date: 10 June 2025. Next inspection due: 10 June 2026. Issue date to tenant: 30 June 2025 (20 days after inspection, within the 28-day Regulation 36 deadline).
Engineer: James Hartley. Gas Safe Registration Number: 123456. Appliance categories held: Central Heating and Hot Water (CHHW), Cookers and Hobs (CH). Appliance 1: Location: kitchen, Type: combination boiler, Make: Vaillant, Model: ecoTEC Plus 835, Serial Number: 217834659. Flue type: room-sealed balanced flue. Flue flow test: satisfactory. Ventilation: not required (room-sealed). Safety devices tested: pressure relief valve, automatic gas valve. Both satisfactory. Operating pressure: 20 mbar. Combustion analysis: CO 12 ppm, CO2 9.1%, CO/CO2 ratio 0.0013. Classification: Safe to use.
Gas tightness test: carried out using U6 meter. Test pressure applied. No perceptible movement after two minutes. Result: satisfactory. Certificate signed by James Hartley on 10 June 2025. Emailed to Ms A. Harrison on 30 June 2025 (read receipt retained). Copy emailed to Mr D. Patel on the same date. Engineer's copy retained in digital job record. This is a clean, legally compliant CP12. Every mandatory field is complete. The inspection date and issue date are both recorded. The 28-day window is met. The appliance classification is supported by specific combustion readings.
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