Gas Safety Checks, CP12 Certificates, and Carbon Monoxide Alarms — Landlord Obligations and Gas Safe Register Requirements for UK Engineers

Annual gas safety checks are a legal requirement for landlords under the Gas Safety (Installation and Use) Regulations 1998. Every rental property with gas appliances must be inspected by a Gas Safe registered engineer, and a CP12 certificate (Landlord Gas Safety Record) issued. Failure to comply carries a maximum six-month prison sentence and an unlimited fine. This guide covers what the inspection covers, CP12 record-keeping, carbon monoxide alarm requirements under Part J of the Building Regulations, and the products that Gas Safe engineers need on every job.

What Is a CP12 Certificate?

CP12 stands for CORGI Proforma 12 — the legacy form name retained in common usage. The correct name is now Landlord Gas Safety Record (LGSR), issued under Regulation 36 of the Gas Safety (Installation and Use) Regulations 1998. The record confirms that all gas appliances, flues, and pipework in a rental property have been inspected by a Gas Safe registered engineer and found to be safe.

Key legal requirements:

• Annual inspection — must occur every 12 months
• Copy to existing tenants within 28 days of inspection
• Copy to new tenants before they move in, or within 28 days of inspection if they move in before the inspection date
• Records must be kept for two years
• If a new boiler or gas appliance is installed, the installation records serve as the first gas safety check

The engineer must be Gas Safe registered and their registration must cover the specific appliance categories being inspected (e.g., domestic boilers, gas fires, cookers).

What Does a Gas Safety Check Cover?

A landlord gas safety inspection covers all gas appliances and installation pipework within the property. The CP12 inspection checklist includes:

Gas Appliances

• Boiler: Visual inspection, burner operation, heat exchanger condition, flue integrity, gas pressure, safety cutout operation. See also: Boiler Servicing and Annual Central Heating Maintenance (guide coming soon)
• Gas fires (open-flued and balanced-flue): Combustion analysis, spillage test, fireguard integrity
• Gas cookers and hobs: Burner operation, igniter function, stability bracket check
• Gas water heaters and back boilers: Flue integrity, heat exchanger condition, pressure relief valve check

Flues and Ventilation

• Flue integrity and termination — no blockages, correct clearances from openings
• Adequate ventilation for open-flued appliances — air vents not blocked
• Fan-assisted flue operation and pressure differential switch function
• Balanced flue terminal clearances — no obstructions, pest guards intact

See: Boiler Flues and Balanced Flue Systems

Gas Pipework

• Visual inspection of all accessible pipework — corrosion, mechanical damage, unsupported runs
• Gas tightness test using a calibrated manometer (U-gauge or electronic) — standing pressure and working pressure tests
• Emergency control valve (ECV) operation
• Meter condition and meter connection

Safety Devices

• Flame failure devices (FFDs) — operation tested on all appliances
• Overheat thermostats and pressure relief valves — condition checked
• Carbon monoxide alarms — presence and function (see below)

Gas Tightness Testing

A gas tightness test is mandatory at every gas safety inspection. The procedure follows IGE/UP/1B (domestic natural gas installations) or equivalent:

1. Isolate all appliances at their isolation valves
2. Connect a manometer at the test point on the gas meter outlet or emergency control valve
3. Pressurise the system to working pressure (typically 21 mbar for domestic natural gas)
4. Allow pressure to stabilise (1–2 minutes)
5. Record standing pressure over a 2-minute period — no pressure drop permitted
6. Turn on all appliances to check working pressure (should remain ≥17 mbar at maximum demand)
7. Any pressure drop indicates a leak — locate using approved leak detection fluid, repair, and retest

PTFE thread seal tape is essential for remaking gas fittings on compression joints and threaded connections. Ensure the tape is approved for gas use (white PTFE is standard for natural gas; yellow tape is specifically designed for gas and is preferred by many engineers).

Carbon Monoxide Alarms — Building Regulations Part J

Carbon monoxide (CO) is produced by incomplete combustion of any fossil fuel — gas, oil, solid fuel. It is colourless, odourless, and lethal at concentrations above approximately 1,500 ppm over one hour.

Legal Requirements

Since 1 October 2022, the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 extended CO alarm requirements in England to include all rooms with a fixed gas appliance (not just solid fuel). Requirements for rental properties:

• A CO alarm must be installed in every room with a fixed combustion appliance (boiler, gas fire, etc.) — excludes gas cookers
• Smoke alarms required on every floor
• Alarms must be tested and working at the start of each tenancy
• Landlords must repair or replace faulty alarms following tenant notification

In Scotland (Housing (Scotland) Act 2014 regulations from February 2022): interlinked CO alarms required in rooms with a carbon-fuelled appliance, in rooms connected to those rooms, and in circulation spaces.

In Wales: similar requirements under the Renting Homes (Wales) Act 2016 regulations.

CO Alarm Types

CO Alarm Placement

• Position on the ceiling or high on the wall (CO is approximately the same density as air but rises with warm combustion gases)
• At least 1–3 metres from the appliance — not directly above
• Not in dead air spaces (ceiling corners, behind furniture)
• Not in kitchens directly above cooking appliances — condensation and grease can affect sensor life
• Boiler cupboard: one alarm inside if the boiler is enclosed, plus one in the adjacent room
• Replace alarms at end of their rated life (typically 7–10 years)

Testing CO Alarms

Test function with the test button monthly. Full performance testing requires CO gas in a test atmosphere — most domestic engineers rely on manufacturer test buttons, which confirm the circuit but not the sensor response. If a tenant reports symptoms (headache, nausea, dizziness), treat as a potential CO incident: evacuate, call Gas Emergency (0800 111 999), ventilate. Do not re-enter until confirmed safe.

Completing the CP12 Record

A completed Landlord Gas Safety Record must include:

• Engineer's Gas Safe registration number and company details
• Date of inspection
• Property address
• Description of each appliance inspected: location, type, maker, model (where possible)
• Defects found and action taken (any immediately dangerous [ID] appliances must be labelled and isolated)
• Result of gas tightness test (pass/fail)
• Flue flow/spillage test results
• CO alarm: present/absent, tested, result
• Inspector's signature

Immediately Dangerous and At Risk Classifications

• Immediately Dangerous (ID): The appliance poses an immediate risk to life. Isolate, label, and record. Inform landlord or property manager in writing immediately. The appliance must not be used until repaired and re-inspected.
• At Risk (AR): The appliance is not immediately dangerous but has a defect that could become dangerous. Advise landlord/user in writing. Recommend repair within a specified timeframe.
• Not to Current Standards (NCS): The appliance does not meet current installation requirements but is not unsafe. Record for information.

New Tenancy Requirements

From 6 April 2018, landlords must provide tenants with a copy of the gas safety record before they occupy the property or within 28 days of the check being carried out. This can be provided electronically (email) if the tenant agrees.

Letting agents acting for landlords take on the landlord's gas safety obligations unless a written management contract specifies otherwise. Both the landlord and the agent can be prosecuted if the obligations are not met.

Differences: Annual Service vs Gas Safety Check

The CP12 inspection is not the same as an annual boiler service, though many engineers combine them:

See also: Boiler Servicing and Annual Central Heating Maintenance for full boiler service procedures including inhibitor dosing, descaling, and combustion analysis.

Gas Engineer Tools and Consumables

Every Gas Safe engineer should carry:

• Calibrated manometer (electronic or U-gauge) — for gas tightness testing
• Combustion analyser — for flue gas analysis (CO, CO/CO₂ ratio, O₂, efficiency)
• CO personal safety monitor — worn by the engineer on every job
• Leak detection fluid — for identifying leaks at fittings
• PTFE thread seal tape — for remaking gas-rated threaded connections
• CO alarm test gas — for functional testing of customer CO alarms
• Spare CO alarms — for fitting on advisory or compliance visits

Product Cards

Frequently Asked Questions

Can a landlord carry out their own gas safety check?

No. Gas safety checks and CP12 certificates can only be issued by engineers registered with the Gas Safe Register. Landlords who carry out their own gas work risk prosecution, invalidate their insurance, and endanger their tenants.

What happens if a landlord doesn't have a valid CP12?

Local authorities can prosecute under the Gas Safety Regulations, with penalties of up to six months imprisonment and/or an unlimited fine. Landlords cannot serve a Section 21 eviction notice without providing tenants with a valid gas safety record. Some mortgage lenders and insurers also require current CP12 records.

How long does a gas safety check take?

A typical domestic inspection takes 30–60 minutes for a single gas appliance (boiler) in a straightforward property. Larger properties with multiple appliances (boiler, gas fires, gas cooker) typically take 1–2 hours.

Do gas-only properties need a CO alarm?

Yes — since October 2022, all rental properties with a fixed gas appliance (boiler, gas fire) require a CO alarm in those rooms. This applies to properties with gas only, not just those with solid fuel. Gas cookers are excluded from the requirement.

Can CO alarms be rented separately from the property?

No legal requirement for separate rental — the alarm is a fixture of the property. Landlords provide and maintain the alarms; tenants must not tamper with or remove them.

What is the difference between Gas Safe and CORGI?

CORGI (Council for Registered Gas Installers) was the UK's gas registration body until April 2009. Gas Safe Register replaced CORGI as the official body for all gas work in Great Britain. Northern Ireland has a separate scheme (RGII). All references to "CORGI-registered" in older documentation should be read as "Gas Safe registered".

Summary

CP12 gas safety checks are an annual legal obligation for landlords — covering all gas appliances, flues, pipework, and safety devices. Gas Safe registered engineers must issue the certificate and provide copies to tenants. Carbon monoxide alarms are now legally required in rooms with fixed combustion appliances in all rental properties in England, Scotland, and Wales. Every gas engineer should carry CO alarms for advisory and compliance installs on every job.

Related guides:

• Boiler Flues and Balanced Flue Systems
• Smoke Alarms and Heat Detectors — BS 5839-6
• Central Heating Controls — Room Thermostats, Programmers, and TRVs
• Condensate Pipes and Frozen Condensate Repair

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