Summary
Carbon monoxide is colourless, odourless and non-irritating, which is why regulation — rather than occupant awareness — is the primary line of defence against CO poisoning in UK homes. Around 30-40 accidental CO deaths and several thousand hospital attendances are recorded in England and Wales each year, the majority linked to faulty or poorly maintained gas appliances, blocked flues, and solid fuel appliances used in unventilated spaces.
For tradespeople, CO alarms sit at the intersection of two separate obligations that are easy to conflate: what the alarm itself must be capable of (the product standard, BS EN 50291-1), and where the law requires one to be fitted (Building Regulations for new/replacement appliance work, and the Smoke and CO Alarm Regulations for landlords). A compliant alarm fitted in a non-compliant location, or a correctly-sited alarm that doesn't meet the product standard, both fail an inspection.
Landlord duties changed materially in 2022 — the amendment to the Smoke and Carbon Monoxide Alarm (England) Regulations extended CO alarm requirements from solid-fuel-only rooms to any room with a fixed combustion appliance (with the specific exclusion of gas cookers), and added a duty to repair or replace a faulty alarm as soon as reasonably practicable once informed. This closed a gap that had left the majority of gas-heated rental properties without a legal CO alarm requirement.
Key Facts
- BS EN 50291-1:2018+A1:2023 — the product standard for CO alarms sold and installed in UK domestic premises; check for this marking on the alarm body.
- BS EN 50292:2019 — separate guidance standard covering positioning, selection and maintenance — see co alarm positioning for the detailed siting rules (distances, heights, dead-air zones).
- The Smoke and Carbon Monoxide Alarm (England) Regulations 2015 — as amended by the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, effective 1 October 2022.
- 2022 amendment scope — extended the CO alarm requirement from "rooms with a solid fuel appliance only" to "any room used as living accommodation containing a fixed combustion appliance" (excluding gas cookers).
- Landlord duty — install alarm(s) before a new tenancy starts; check they are in working order at the start of each new tenancy; repair or replace as soon as reasonably practicable once informed of a fault.
- Enforcement — local housing authorities can issue a remedial notice, and non-compliance can result in a civil penalty of up to £5,000, plus potential impact on the landlord's ability to use Section 21 eviction proceedings.
- Building Regulations Approved Document J — requires a CO alarm for new or replacement solid fuel appliances, and (in most cases) new or replacement gas appliances that are not room-sealed, and oil-fired appliances.
- Room-sealed gas appliances — not always required under Part J since they draw combustion air from and discharge to outside, but strongly recommended and, for rented property, required under the 2022 Smoke and CO Alarm Regulations regardless.
- Alarm types — battery (sealed, 7-10 year life, non-replaceable cell), mains-wired with battery backup, and smart/connected alarms with app alerts — all must meet BS EN 50291-1 regardless of power source.
- Combined smoke + CO alarms — exist and are convenient for combi appliance rooms, but should still be sited per CO alarm rules (lower, close to appliance) rather than smoke alarm rules (high, central) — a genuine dual-optimum position rarely exists, so manufacturer guidance should be followed for the specific unit.
- End-of-life indication — sealed alarms give an audible chirp at end of sensor life (typically 7-10 years from manufacture date printed on the unit) — this is not a low-battery warning, it means the sensor itself needs replacing.
- Scottish requirements — under the Housing (Scotland) Act 1987 Tolerable Standard, as extended by the 2019 Order and in force from 1 February 2022, a CO alarm is required in any room with a fixed combustion appliance, applying to both owner-occupied and rented property, not just private rentals.
- Wales and Northern Ireland — broadly aligned via Building Regulations Part J (Wales) and Part L/Part F (Northern Ireland), with separate landlord-specific regulations under devolved housing legislation.
- HMOs — CO alarm requirements apply per room with a combustion appliance, in addition to the separate and more extensive smoke alarm/fire detection requirements for HMOs under the Housing Act 2004 and licensing conditions.
- Compliance responsibility — for landlords, ultimate legal responsibility for CO alarm compliance sits with the landlord even where an installer/engineer fitted or serviced the appliance; installers should document alarm fitting/testing on the job certificate to protect against liability disputes.
Quick Reference Table — Who Needs a CO Alarm, Where
Spending too long on quotes? squote turns a 2-minute voice recording into a professional quote.
Try squote free →| Property/Situation | CO Alarm Required? | Governing Rule |
|---|---|---|
| Owner-occupied home, new/replacement solid fuel appliance | Yes | Building Regs Part J |
| Owner-occupied home, new/replacement gas boiler (not room-sealed) | Yes | Building Regs Part J |
| Owner-occupied home, room-sealed combi boiler | Not mandatory, strongly recommended | Part J (exemption for room-sealed) |
| Private rented, any room with fixed combustion appliance (excl. gas cooker) | Yes | Smoke & CO Alarm Regs 2015 (amended 2022) |
| Private rented, room-sealed combi | Yes (since 2022 amendment) | Smoke & CO Alarm Regs 2022 amendment |
| Private rented, gas cooker only, no other appliance | Not required (cooker excluded) | Smoke & CO Alarm Regs 2015 |
| HMO, room with fixed combustion appliance | Yes | Smoke & CO Alarm Regs + HMO licensing conditions |
| Scotland, any tenure, room with fixed combustion appliance | Yes | Tolerable Standard 2019 |
| Existing gas boiler with no appliance work being carried out | No new statutory trigger (owner-occupied), but landlord duty may still apply | Part J only triggers on new/replacement work |
Detailed Guidance
Distinguishing the product standard from the siting rules
Two separate BS EN standards are relevant and frequently confused on site:
- BS EN 50291-1 governs what the alarm itself must do — sensitivity, response time, sounder volume, durability. This is a manufacturing/product standard; as an installer you check it's printed on the unit, you don't calculate anything against it.
- BS EN 50292 governs where and how to install it — horizontal distance from the appliance, height below ceiling, dead-air zone avoidance, number of alarms needed in multi-room/multi-storey properties. See co alarm positioning for the full distance/height reference tables and room-by-room siting guide.
Landlord duties in detail
Since the October 2022 amendment, private landlords in England must:
- Ensure a CO alarm is fitted in any room used as living accommodation that contains a fixed combustion appliance — this now includes gas boilers, gas fires, and other gas/oil/solid-fuel fixed appliances, not just solid fuel as before. Gas cookers remain specifically excluded from triggering the requirement.
- Ensure alarms are in working order at the start of each new tenancy — a landlord or their agent must check this, not simply assume the previous tenant's alarm still works.
- Repair or replace an alarm as soon as reasonably practicable once informed by the tenant (or otherwise becoming aware) that it is faulty or missing.
- Keep records — while the regulations don't mandate a specific record-keeping format, a dated compliance certificate or checklist from the fitting/checking engineer is strong practice and standard evidence in the event of a dispute or incident.
Landlords who don't comply can be issued a remedial notice by the local housing authority; failure to act on the notice within 28 days can result in a civil penalty of up to £5,000. This sits alongside — and is separate from — any liability arising from an actual CO incident, which would be assessed under health and safety and potentially manslaughter/gross negligence law depending on severity.
Building Regulations trigger points (Part J)
Part J only applies when appliance work is actually being carried out — it does not retrospectively require alarm fitting to an existing, unmodified installation. The triggers are:
- Installing a new solid fuel appliance (stove, open fire with a flue).
- Replacing an existing solid fuel appliance.
- Installing or replacing most gas appliances that are not room-sealed (open-flued gas fires, older gas boilers).
- Installing or replacing oil-fired appliances.
Room-sealed gas boilers (most modern combis) fall outside the mandatory Part J trigger in owner-occupied property, though fitting an alarm anyway remains best practice and is a straightforward addition to any boiler swap quote — cheap goodwill that also covers the installer against comeback.
Choosing alarm type for the job
| Type | Power | Typical Life | Best For |
|---|---|---|---|
| Sealed battery | Non-replaceable cell | 7-10 years | Standard retrofit, no wiring access needed |
| Mains-wired + battery backup | Hardwired, backup cell | 10 years+ (sensor still time-limited) | New build/rewire, interlinked systems |
| Smart/connected | Battery or mains | 7-10 years (sensor) | Landlords wanting remote fault notification, HMOs |
| Combined smoke + CO | Sealed battery typically | 7-10 years | Space-constrained rooms, though siting compromise applies |
Whatever the power source, the sensor itself has a fixed service life (7-10 years from manufacture) — mains wiring or smart connectivity doesn't extend sensor life, only power reliability.
Frequently Asked Questions
Do I need to fit a CO alarm every time I service a gas boiler?
Servicing alone doesn't trigger the Part J requirement — that applies to new or replacement appliance installation, not routine servicing. However, checking the presence, position and end-of-life status of any existing CO alarm should be part of every gas safety check, and flagging a missing or expired alarm to the customer/landlord is good practice and, for landlords, may support their compliance duty under the Smoke and CO Alarm Regulations.
Does a gas cooker trigger the landlord CO alarm requirement on its own?
No — gas cookers are specifically excluded from the definition of "fixed combustion appliance" for the purposes of the Smoke and Carbon Monoxide Alarm Regulations, even after the 2022 amendment. A kitchen with only a gas cooker and no other combustion appliance does not legally require a CO alarm under these regulations, though fitting one remains sensible given gas cookers do produce some CO.
What happens if a tenant reports a faulty alarm and the landlord doesn't act?
The landlord is in breach of their duty to repair or replace "as soon as reasonably practicable" once informed. The local housing authority can issue a remedial notice, and continued non-compliance can lead to a civil penalty of up to £5,000. Documenting the report date and any landlord response is important evidence if a dispute or enforcement action follows.
Is a combined smoke and CO alarm a good compromise for a boiler cupboard?
It can work in space-constrained situations, but be aware smoke alarms are optimally sited high/central in a room while CO alarms are optimally sited lower and closer to the appliance (see co alarm positioning) — a single combined unit is a compromise on one or both functions. Follow the specific manufacturer's siting guidance for that combined unit rather than applying single-purpose alarm rules, and consider whether separate dedicated alarms would serve the room better.
Regulations & Standards
BS EN 50291-1:2018+A1:2023 — Electrical apparatus for the detection of carbon monoxide in domestic premises — product standard.
BS EN 50292:2019 — Guide on the selection, installation, use and maintenance of CO alarms — see co alarm positioning for detail.
The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, as amended by the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 — landlord duties for private rented sector.
Building Regulations Approved Document J (England & Wales) — Combustion appliances and fuel storage systems, alarm requirement triggers for new/replacement appliance work.
Housing Act 2004 — HMO licensing conditions, including fire and CO safety requirements.
Housing (Scotland) Act 1987, Tolerable Standard (extended 2019, in force from 1 February 2022) — Scottish CO alarm requirements across all tenures.
Gas Safety (Installation and Use) Regulations 1998 — general duties on gas engineers, including CO risk awareness.
gov.uk — Smoke and carbon monoxide alarms: explanatory booklet for landlords
gov.uk — Approved Document J: Combustion appliances and fuel storage systems
co alarm positioning — detailed siting distances, heights and room-by-room placement rules to BS EN 50292
wood burner installation pricing guide — CO alarm requirement in solid fuel appliance install scope
gas safety certificate — landlord CP12 gas safety certificate duties, related but separate obligation
cookers bayonet fittings — gas cooker connections and why cookers are excluded from the CO alarm trigger