Carbon Monoxide Alarm Regulations When Selling

Carbon monoxide alarms sit at the intersection of safety law, building regulations, and buyer expectation. The legal framework for sellers is less straightforward than many assume: there is no single rule that says you must have a working CO alarm to sell your home, but the practical reality is that Building Regulations, buyer surveys, solicitor enquiries, and mortgage lender requirements all converge to make adequate carbon monoxide detection an effective necessity during any property sale involving gas, oil, or solid fuel appliances.

This guide explains exactly which regulations apply to sellers, what they require, how CO alarms interact with the conveyancing process, and what steps you should take before listing your property to prevent alarm-related issues from causing delays or complications.

The legal framework for carbon monoxide alarms in England

Carbon monoxide alarm requirements in England come from two separate and complementary sources: the Building Regulations, which apply to all properties where relevant building work has been carried out, and the landlord regulations, which apply specifically to rented residential properties. Understanding which applies to your situation is the first step.

Building Regulations Approved Document J

Approved Document J is the section of the Building Regulations for England that covers combustion appliances and fuel storage systems. Since October 2010, it has required that a carbon monoxide alarm be fitted whenever a new or replacement fixed combustion appliance is installed in a dwelling. This applies regardless of whether the property is owner-occupied or rented, and regardless of fuel type. The requirement is triggered by the installation of the appliance, not by the tenure of the occupant.

Fixed combustion appliances covered by this requirement include:

• Gas boilers (combi, system, and conventional heat-only boilers)
• Gas fires (open-flued and room-sealed, including decorative gas fires)
• Oil-fired boilers and oil-fired stoves
• Wood-burning stoves and multi-fuel stoves
• Open fireplaces burning solid fuel (coal, wood, peat)
• Biomass boilers

Gas cookers and gas hobs are explicitly excluded from the requirement. The reasoning is that cooking appliances are used briefly in well-ventilated conditions, which does not present the same sustained carbon monoxide risk as a heating appliance running for hours at a time in a closed room.

The alarm must be installed in the same room as the appliance, conforming to BS EN 50291-1 (the British and European standard for carbon monoxide alarms for domestic use). It must be positioned between 1 and 3 metres horizontally from the appliance at head height. For the full building regulations documentation context, see our guide on what is a property certificate pack.

Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022

The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, as amended by the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, impose specific duties on landlords of residential properties in England. These regulations came into full force on 1 October 2022 and do not apply to owner-occupier sellers.

Under the 2022 regulations, landlords must install a carbon monoxide alarm in every room that contains a fixed combustion appliance, excluding gas cookers. This extends the previous 2015 requirement, which only covered solid fuel appliances, to include gas and oil appliances as well. A landlord who fails to comply after receiving a remedial notice from the local housing authority can face a civil penalty of up to £5,000.

If you are selling a property that has been rented out, your buyer's solicitor will expect evidence of compliance with these regulations. For the landlord obligations that form part of the wider sale documentation, see our guide on gas safety certificates when selling.

What owner-occupier sellers need to know

As an owner-occupier, your position on carbon monoxide alarms when selling depends on whether building work that triggered an Approved Document J requirement has been carried out on the property.

If a boiler, stove, or gas fire has been installed or replaced

If any fixed combustion appliance in your property has been installed or replaced since October 2010, a carbon monoxide alarm should have been fitted in that room as part of the installation. This is a building regulations requirement, and the installer (typically a Gas Safe registered engineer for gas appliances, or a HETAS-registered installer for solid fuel appliances) should have included the alarm as part of the job.

If the installation was done without a CO alarm, this is a building regulations compliance gap. The buyer's solicitor will check building control records and may query whether the installation was signed off correctly. You have several options:

• Install the correct CO alarm. For most sellers, simply installing a conforming CO alarm before listing resolves the issue. The alarm must meet BS EN 50291-1, be installed in the correct position, and be within its service life.
• Obtain evidence of compliance. If the engineer who installed the appliance can confirm in writing that a CO alarm was fitted (or provide a copy of the completion documentation), this may be sufficient for the buyer's solicitor.
• Indemnity insurance. In some cases where retrospective documentation is unavailable, indemnity insurance can be obtained to cover the risk of enforcement action. This is discussed in more detail in our guide on hidden costs of selling a house.

If no notifiable building work has been carried out

If the property has had no notifiable building work involving combustion appliances — for example, if the boiler and any gas fires are the original installation and have never been replaced — there is no building regulations requirement to have a CO alarm. The Approved Document J requirement is triggered by installation, not by the passage of time.

Even so, the practical reality is that buyers, surveyors, and mortgage lenders have all become more attuned to carbon monoxide risks following high-profile public awareness campaigns and the extension of landlord CO alarm requirements. A buyer purchasing a property with a gas boiler but no CO alarm will almost certainly ask about it, and their surveyor is likely to flag the absence in their report.

Given that a carbon monoxide alarm costs as little as £15 to £30 and takes minutes to install, there is no good reason for a seller not to fit one before going to market.

How CO alarms interact with the conveyancing process

Carbon monoxide alarms come up at several stages of a property transaction. Understanding each touchpoint helps you prepare effectively.

The TA6 Property Information Form

The TA6 Property Information Form is the primary disclosure document completed by sellers. Section 7 covers services and utilities, including the heating system and hot water installation. Your solicitor will ask you to describe the type and age of your boiler and any other heating appliances, and to confirm what safety certificates and documentation are available.

If your property has gas appliances, you should confirm in the TA6 whether carbon monoxide alarms are fitted, their approximate age, and whether they were installed as part of building regulations compliance when an appliance was fitted. Providing this information clearly and attaching a gas safety certificate reduces the likelihood of follow-up enquiries from the buyer's solicitor.

Conveyancing enquiries

If the TA6 does not include clear information about CO alarms, or if the buyer's solicitor considers the position ambiguous, they may raise a specific enquiry asking whether CO alarms are fitted and, if so, whether they were installed in compliance with Building Regulations Approved Document J. Responding to additional enquiries adds time to the transaction — sometimes by one to two weeks per round.

If building work involved a combustion appliance but there is no evidence of a CO alarm being fitted, the solicitor may also ask about building control sign-off and may request sight of the completion certificate for the relevant work. If this documentation is missing or incomplete, the buyer may seek indemnity insurance as part of the transaction.

The buyer's survey

Surveyors conducting a homebuyer's report or a full building survey will note the presence or absence of carbon monoxide alarms in rooms with combustion appliances. They will also check whether alarms appear to be within their service life and whether they are correctly positioned. If alarms are missing, expired, or incorrectly sited, the surveyor will flag this as a safety recommendation in their report, typically recommending that the buyer arranges for compliant CO alarms to be installed.

A surveyor's recommendation about CO alarms can have two knock-on effects: it may give the buyer grounds to renegotiate the price (on the basis that remedial work is needed), or it may prompt the buyer's mortgage lender to impose a retention until the issue is resolved.

Mortgage lender conditions

Most mortgage lenders do not routinely include CO alarm requirements in their standard conditions. However, if the surveyor's report flags concerns about carbon monoxide safety — particularly if there are gas appliances present and no CO alarms — the lender may impose a condition requiring evidence that alarms have been installed before releasing mortgage funds. This can add days or weeks to the completion timeline. Ensuring CO alarms are in place before you list removes this risk entirely.

Landlord obligations when selling

If you are a landlord selling a property that is currently tenanted or has previously been rented out, the carbon monoxide alarm obligations are more prescriptive.

Under the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, you must have a CO alarm installed in every room containing a fixed combustion appliance (excluding gas cookers). This includes:

• The room where the gas boiler is located (often a kitchen, utility room, or airing cupboard)
• Any room with a gas fire, gas room heater, or decorative gas fire
• Any room with a wood-burning stove or multi-fuel stove
• Any room with an oil-fired appliance

The buyer's solicitor will ask for evidence of compliance when purchasing a rental property. If you are selling with a tenant in place, you should be able to demonstrate that:

• CO alarms were in place on the first day of the current tenancy
• Any alarms reported as faulty by the tenant were repaired or replaced promptly
• The alarms are within their recommended service life

Alongside CO alarm compliance, a valid gas safety certificate and evidence of a current boiler service record are essential documents for any landlord sale. Together, these demonstrate a comprehensive approach to gas safety that will satisfy the buyer's solicitor with minimal additional enquiries.

Choosing the right carbon monoxide alarm

Not all CO alarms are equal, and buying the correct type matters for both safety and compliance.

Standard compliance: BS EN 50291-1

Any carbon monoxide alarm installed to comply with Building Regulations Approved Document J or the landlord regulations must conform to BS EN 50291-1, which is the British Standard (and harmonised European Standard) for electrical apparatus for the detection of carbon monoxide in domestic premises. Alarms sold in UK hardware stores and by reputable suppliers will carry the BS EN 50291-1 marking. Do not use industrial CO monitors or CO detectors designed for non-domestic settings, as these operate to different thresholds.

Types of CO alarm

Where to place the alarm

Correct positioning is as important as buying the right alarm. Guidance from Approved Document J and BS EN 50292 (the standard for the selection, installation, use, and maintenance of CO alarms) specifies the following:

• Same room as the appliance. The alarm must be in the same room as the combustion appliance, not in an adjacent hallway or corridor.
• Head height. Mount the alarm on a wall or ceiling at approximately head height (at least 1.5 metres above floor level). CO disperses relatively evenly because it is close in weight to air, so ceiling mounting is acceptable.
• 1 to 3 metres from the appliance. Position the alarm between 1 and 3 metres horizontally from the appliance. Closer than 1 metre risks nuisance alarms from normal start-up emissions.
• Not in enclosed spaces. Avoid placing alarms inside cupboards, behind furniture, or in poorly ventilated corners where CO may not reach the sensor quickly.
• Not directly above the appliance. Mounting directly above an appliance — for example, directly above a boiler on the ceiling — risks false activations from normal flue-gas drafts.
• Not near windows or vents. Fresh air from a nearby window or extractor fan can dilute CO before it reaches the sensor, reducing the alarm's effectiveness.

Checking and replacing existing alarms before listing

If your property already has carbon monoxide alarms, it is not enough simply to confirm they exist. Buyers, surveyors, and solicitors will expect them to be functional and within their service life. Before listing, you should:

1. Test every CO alarm. Press the test button on each alarm. A working alarm will emit a continuous beep or siren. If the alarm does not sound, replace it.
2. Check the manufacture and expiry date. The end-of-life date is usually printed on the back or underside of the unit, alongside the manufacture date. An alarm past its expiry date must be replaced, even if it still sounds when tested — the electrochemical sensor degrades over time regardless of the battery condition.
3. Check the positioning. Confirm that each alarm is in the same room as the relevant appliance and is positioned correctly according to the guidance above.
4. Document what you have. Note the make, model, and installation date of each alarm and include this information when completing the TA6 form. If the alarm was installed as part of a boiler or stove installation, keep the installation certificate or any commissioning documentation.

For context on all the safety and compliance documentation a buyer will expect you to have assembled before exchange, our guide on checking the Gas Safe Register explains how to verify the credentials of the engineers who have worked on your property.

Carbon monoxide alarm requirements in Scotland and Wales

The regulations described above apply to England. Scotland and Wales have their own requirements.

Scotland

In Scotland, the requirements are significantly more stringent and apply to all homes, not just those with recent building work or rental properties. Since February 2022, the Tolerable Standard for housing in Scotland requires:

• Interlinked smoke alarms in the living room and hallways on every level
• An interlinked heat alarm in the kitchen
• A carbon monoxide detector in any room with a carbon-fuelled appliance

This applies to all homes regardless of tenure — including owner-occupied properties being sold. If you are selling a property in Scotland without a CO alarm in rooms with carbon-fuelled appliances, the property does not meet the Tolerable Standard and a buyer's solicitor will raise this during the transaction.

Wales

In Wales, Building Regulations Part J applies in the same way as in England, requiring a CO alarm when a new or replacement combustion appliance is installed. The Renting Homes (Wales) Act 2016 imposes CO alarm duties on landlords in Wales, similar to the 2022 regulations in England. Owner-occupier sellers in Wales face the same practical position as those in England: no standalone legal duty to install CO alarms for the sale, but Building Regulations compliance requirements where combustion appliances have been installed.

Cost of carbon monoxide alarm compliance

The cost of ensuring your CO alarms are compliant before listing is low compared with the potential cost of delays and renegotiations:

For most properties with one or two combustion appliances, fitting compliant CO alarms before listing costs £30 to £60 in materials and a few minutes of time. This is a negligible outlay compared with the one to two weeks that a single round of conveyancing enquiries can add to a transaction, or the cost of a price reduction negotiated on the back of a surveyor's report.

Practical seller checklist

Use this checklist to ensure CO alarm compliance is in order before you list:

1. Identify every room in the property that contains a fixed combustion appliance (gas boiler, gas fire, wood burner, oil boiler — but not gas hob or cooker).
2. Check whether a CO alarm is present in each of those rooms. If not, install one conforming to BS EN 50291-1.
3. Test each CO alarm using the test button and confirm it sounds correctly.
4. Check the manufacture and end-of-life date printed on each alarm. Replace any that are expired or within 12 months of expiry to ensure they remain valid throughout the sale timeline.
5. Confirm each alarm is correctly positioned: same room as the appliance, head height, 1 to 3 metres horizontally from the appliance, not in an enclosed space or near a window.
6. Note the details of each alarm (make, model, date installed) and include them when completing the TA6 Property Information Form.
7. If a boiler or other appliance has been installed or replaced in the last 15 years and you cannot locate the building control completion certificate or installation documents, speak to your solicitor about whether any further steps are needed.
8. If you are a landlord, confirm compliance with the 2022 regulations and retain records for the buyer's solicitor.

Sources

• Building Regulations Approved Document J (Combustion Appliances and Fuel Storage Systems) — GOV.UK
• Smoke and Carbon Monoxide Alarm (England) Regulations 2015 — legislation.gov.uk
• Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 — legislation.gov.uk
• BS EN 50291-1:2018 — Electrical apparatus for the detection of carbon monoxide in domestic premises — BSI
• BS EN 50292:2013 — Electrical apparatus for the detection of carbon monoxide in domestic premises: guide for selection, installation, use, and maintenance — BSI
• Health and Safety Executive (HSE) — Carbon monoxide: the silent killer, hse.gov.uk
• Gas Safe Register — Carbon monoxide safety guidance, GasSafeRegister.co.uk
• Scottish Government — Tolerable Standard: fire and carbon monoxide alarms, gov.scot
• Law Society — Property Information Form (TA6), 4th edition

Frequently asked questions