In Wales, Approved Document J (2010 edition incorporating 2010 and 2024 amendments) has said since 6 January 2025 that where a new or replacement fixed flued combustion appliance of any fuel, including gas, oil and solid fuel, is installed in a dwelling, a carbon monoxide alarm should be provided.

What changed and when

The Welsh Government’s circular WGC 004/2024, issued on 4 October 2024, announced amendments to Approved Document J (Combustion appliances and fuel storage systems) in relation to requirement J3, “Warning of release of carbon monoxide”. The changes apply to buildings and building work in Wales and came into force on 6 January 2025. New paragraphs 1.24 to 1.30 deal with alarms where flued fixed combustion appliances of any fuel type are installed, and they replace earlier paragraphs that covered solid fuel appliances only.

This guide covers Wales only. England has its own version of Approved Document J, which is dealt with in a separate guide on this site.

Which appliances trigger an alarm

Paragraph 1.24 says that where a new or replacement fixed flued combustion appliance of any fuel type, meaning oil, gas (including LPG) and solid fuel, is installed in a dwelling, a carbon monoxide alarm should be provided. The paragraph expressly includes fixed flued cookers. A replacement boiler is therefore within scope, and so is a new boiler in a home that never had one.

Which rooms need an alarm

Paragraph 1.25 says an alarm is required in every space containing a fixed combustion appliance, including connected spaces such as attached garages and loft spaces and including a fixed flued appliance used for cooking. An alarm is also required in high-risk accommodation, defined as a bedroom or principal habitable room, for example a living room, where a flue serving a combustion appliance passes through the room.

Type of alarm and where it goes

Alarms should comply with BS EN 50291-1:2018, include an integral sounder and be powered by a battery designed to last the working life of the alarm, with a warning when that life is due to end. Mains-powered Type A alarms with fixed wiring, not plug-in types, are allowed if they have a sensor failure warning. BS EN 50292:2023 and the manufacturer’s instructions give further siting advice.

Unless the manufacturer says otherwise, an alarm should be ceiling mounted at least 300mm from any wall, or wall mounted at least 150mm below the ceiling and higher than any door or window. In the room with the appliance it should be between 1m and 3m from it. Paragraph 1.30 lists places to avoid, including enclosed spaces such as cupboards or behind curtains, positions obstructed by furniture, directly above a sink, next to a door, window, extract fan or air vent, in temperatures below minus 10°C or above 40°C unless designed for it, where dust may block the sensor, in damp locations and near a cooking appliance.

An alarm is not a substitute for good installation

Paragraph 1.27 states that providing an alarm should not be regarded as a substitute for correct installation and regular servicing of combustion appliances, and notes that where an appliance is in a small space it may not be possible to place the alarm inside it.

Transitional rules

The circular says the previous edition continues to apply to work that began before 6 January 2025. It also applies to work where a building notice, initial notice or amendment notice was given, or full plans were deposited, before that date, provided the work starts within three months of 6 January 2025, and to work needing no notification that starts within the same three months. Anything started later falls under the amended guidance.

Certification and other duties

Approved Document J explains that work by a person registered with a competent person self-certification scheme does not need advance notification to a building control body. The occupier must be given a compliance certificate within 30 days of completion, and the building control body must be told within the same period, normally through the scheme operator. The document adds that the Gas Safety (Installation and Use) Regulations apply even to buildings exempt from the Building Regulations.

FAQs

Does an existing boiler need a new alarm?

The guidance is triggered when a new or replacement fixed flued appliance is installed. It does not itself say that existing appliances need an alarm.

Do landlords have a separate duty in Wales?

A Welsh Government consultation document states that, under the Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022, a working alarm must be present in any room with a gas, oil or solid fuel appliance in rented homes.

Does this apply in England?

No. This guide is about the Welsh edition of Approved Document J; England’s document is separate.

Bottom line

In Wales, a new or replacement fixed flued boiler of any fuel now comes with a guidance expectation of carbon monoxide alarms in the appliance space and in certain bedrooms or living rooms crossed by a flue, to BS EN 50291-1:2018. Transitional rules protect work already under way before 6 January 2025. This is general information, not advice on any specific installation; the installer and local building control body can confirm what applies.

Sources

This guide draws on the following primary sources, current as of 21 September 2026:

• Welsh Government, “Approved Document J: Combustion appliances and fuel storage systems, 2010 edition incorporating 2010 and 2024 amendments” (PDF)
• Welsh Government, “Building regulations circular WGC 004/2024: Approved Document J (Combustion appliances and fuel storage systems) 2010 edition incorporating 2010 and 2024 amendments”
• Welsh Government, “Carbon monoxide alarms” (consultation)

Related guides

Best Boiler Deals is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not regulated advice on any specific installation — always confirm the details with a Gas Safe registered engineer.