Quality & Inspections · Mandatory · Completion

Gas Commissioning Certificate

A certificate issued by a Gas Safe registered engineer confirming that gas installations have been commissioned safely.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. Gas Safety Regs 1998 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	Gas Safety (Installation and Use) Regulations 1998
Legal requirement	All gas work must be carried out by a Gas Safe registered engineer — it is a criminal offence for an unregistered person to carry out any gas work
Tightness test	Mandatory before any appliance is connected, conducted in accordance with IGEM/UP/1C
Commissioning record	Required for each appliance — type, supply pressure, burner pressure, gas rate, flue test, combustion analysis (CO/CO²)
CO testing	Critical safety check — carbon monoxide is colourless and odourless, making detection by occupants impossible without instrumentation
Documentation	Gas Safe commissioning record + tightness test record + Landlord's Gas Safety Record (if rented property)

1. Gas Commissioning — Safety Before Service

Gas commissioning is one of the most safety-critical activities on any construction or refurbishment project. An incorrectly commissioned gas appliance can produce lethal carbon monoxide, create a fire or explosion hazard, and endanger every occupant of the building. The legal framework reflects this severity — all gas work must be carried out by a Gas Safe registered engineer, and failure to comply is a criminal offence.

The commissioning process begins with a tightness test of the gas pipework installation, conducted in accordance with IGEM/UP/1C before any appliance is connected. This confirms that the pipework is leak-free at the relevant test pressure. Only after a satisfactory tightness test can appliances be connected and individually commissioned. Commissioning of each appliance involves checking the gas supply pressure, setting the burner pressure, measuring the gas rate, testing the flue for integrity and draught, and conducting a combustion analysis to confirm safe levels of carbon monoxide and carbon dioxide.

Every commissioning activity must be documented on Gas Safe records and provided to the client. For rented properties, a Landlord's Gas Safety Record must also be issued and renewed annually. These records are not optional — they are legal requirements, and their absence is evidence of non-compliance.

Gas Safe registration is a legal requirement

All gas work MUST be carried out by a Gas Safe registered engineer — using an unregistered person is a criminal offence. This applies to installation, maintenance, repair, disconnection, purging, and commissioning. There are no exceptions for minor or simple gas tasks.

2. Gas Commissioning Record Fields

The following table sets out the fields that must be captured on a gas commissioning record. Each field provides evidence of a specific safety check that forms part of the commissioning process.

Field	Description
Engineer details	Name, Gas Safe registration number, and employer details of the registered engineer
Property details	Address and description of the property where the gas work was carried out
Tightness test	Confirmation that the gas pipework installation passed a tightness test to IGEM/UP/1C before appliance connection
Appliance details	Make, model, serial number, type (boiler, water heater, cooker, fire), and location of each appliance
Gas supply	Gas supply pressure measured at the meter (mbar) with all appliances operating
Burner pressure	Burner pressure measured at the appliance test point and compared to manufacturer's specification
Gas rate	Gas rate measured and compared to the appliance data plate to confirm correct operation
Flue test	Flue integrity and draught test results — confirming products of combustion are safely discharged to outside
Combustion analysis	CO and CO² readings from a calibrated flue gas analyser, confirming combustion is within safe parameters
Safety controls	Confirmation that all safety controls (flame supervision, overheat protection, ventilation) are functioning correctly
Appliance result	Pass, fail, or “at risk” / “immediately dangerous” classification for each appliance
Client declaration	Client or occupant acknowledgement that the work has been completed and documentation provided
Gas Safe signature	Signature of the Gas Safe registered engineer confirming all checks and tests were completed

3. Common Mistakes

Not conducting a tightness test before commissioning appliances

The gas pipework installation must pass a tightness test to IGEM/UP/1C before any appliance is connected. Connecting and commissioning appliances on an untested gas supply risks operating on a pipework system with undetected leaks — a fire and explosion hazard.

Not carrying out combustion analysis (CO testing)

Combustion analysis using a calibrated flue gas analyser is essential for confirming that the appliance is burning gas safely. Without CO and CO2 readings, there is no evidence that the appliance is not producing dangerous levels of carbon monoxide. CO is colourless and odourless — it cannot be detected without instrumentation.

Allowing a non-Gas Safe registered person to carry out gas work

It is a criminal offence under the Gas Safety (Installation and Use) Regulations 1998 for any person not registered with Gas Safe to carry out gas work. This includes installation, maintenance, repair, disconnection, purging, and commissioning. Penalties include unlimited fines and up to two years imprisonment.

Not providing documentation to the client

The Gas Safe registered engineer must provide the client with a commissioning record for each appliance, a tightness test record, and (for rented properties) a Landlord's Gas Safety Record. Failure to provide documentation is non-compliant and leaves the client without evidence of safe installation.

Not verifying that the appliance installation has been notified to Gas Safe Register

Gas Safe registered engineers are required to notify certain categories of gas work to the Gas Safe Register. This includes new appliance installations and replacements. The notification creates a record that the work was carried out by a registered engineer and can be verified by the client or subsequent engineer.

4. Frequently Asked Questions

How can I verify that an engineer is Gas Safe registered?▾

Visit gassaferegister.co.uk and search by the engineer's registration number or name. The register shows the engineer's current registration status and the specific categories of gas work they are qualified to carry out. You can also call the Gas Safe Register helpline.

What is a Landlord's Gas Safety Record?▾

A Landlord's Gas Safety Record (formerly CP12) is a mandatory annual safety check record for all gas appliances in rented properties. It must be carried out by a Gas Safe registered engineer and a copy provided to the tenant within 28 days of the check. The landlord must retain the record for two years.

What CO levels are acceptable during commissioning?▾

CO levels below 200 ppm in the flue gases are typically considered acceptable for most domestic appliances, though the exact acceptable range depends on the appliance type and manufacturer's specification. Readings above 1000 ppm indicate a seriously defective appliance requiring immediate action — the appliance must be disconnected or classified as immediately dangerous.

How long must gas commissioning records be kept?▾

The installing company must retain gas work records for a minimum of two years. However, it is strongly recommended that records are retained for the life of the appliance, as they provide evidence of safe installation and commissioning in the event of any future incident or dispute.

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