Guide · Gas Safety
CO alarms and gas appliances: what the rules actually require
Carbon monoxide is the failure mode the whole gas safety regime exists to prevent — yet the alarm rules that back up the annual check are widely misremembered, especially the gas cooker exception and the differences between nations. This guide sets out where CO alarms must be, where they merely should be, and how the alarm duty and the CP12 work together.
Gas Safety
Which rooms must have a CO alarm in England?
Any room used as living accommodation containing a fixed combustion appliance: gas boilers, gas fires, log burners, oil-fired appliances. The regulation's trigger is the appliance, not the fuel — a wood-burning stove demands an alarm exactly as a gas boiler does. The alarm must be present when the tenancy begins, and repaired or replaced promptly once a tenant reports a fault.
The much-quoted exception: an appliance used solely for cooking — the gas cooker or hob — does not by itself trigger the requirement. That is a floor, not advice. A CO alarm near any gas appliance is cheap insurance, and many landlords sensibly fit one in kitchens anyway; the exception only defines what enforcement can demand.
Gas Safety
How do the other nations handle CO?
Scotland requires a carbon monoxide detector wherever there's a fixed combustion appliance or a flue, as part of the wider interlinked-alarm standard applying to all homes. Wales requires CO alarms in rental properties with combustion appliances under the Renting Homes fitness framework. Northern Ireland drives CO protection through fitness standards and building regulations for newer installations.
The practical convergence is stronger than the legal texts suggest: in every nation, a rental with a boiler, fire or stove and no CO alarm is somewhere between non-compliant and indefensible. Specify to the strictest applicable standard and the geography stops mattering.
Gas Safety
Where should a CO alarm actually be positioned?
In the same room as the appliance, following the manufacturer's siting instructions — typically at head height (unlike smoke alarms, which go on ceilings), between roughly one and three metres from the appliance, away from dead air corners, vents and direct sources of steam. Wall-mounted at breathing height or on a shelf per the instructions both work; inside a cupboard with the boiler does not.
Position errors are the commonest CO failure found on checks: alarms in hallways guarding no appliance, alarms directly above hobs (triggering falsely, then removed), alarms still sealed in packaging in a drawer. The alarm protects a room; it must live in that room, positioned to sample the air people breathe.
Gas Safety
How do CO alarms and the CP12 fit together?
They are complementary layers: the annual gas safety check verifies the appliances are burning and venting correctly today; the CO alarm stands guard for the other 364 days, catching the flue blockage, the bird's nest, the seal that fails between checks. Neither substitutes for the other — a pristine CP12 with no alarm leaves the year unguarded; an alarm with no check monitors a system nobody has verified.
Engineers on the annual visit will commonly note missing or expired CO alarms even though the alarm duty is separate from the gas record itself. Treat that note as a gift: same-visit or same-week fitting closes the gap while it's a task, not a finding.
Gas Safety
What counts as a compliant alarm?
A CO alarm meeting the recognised standard (BS EN 50291 for domestic use), standards-marked, within its manufacturer expiry — CO sensors have finite lives, often shorter than smoke sensors — and powered per its design, with sealed long-life battery units the low-maintenance default for rentals. Interlinked CO units are required where Scotland's standard applies and are good practice in larger properties everywhere.
Record three things per unit at fitting and each check: location, test result, expiry date. The expiry discipline matters more for CO than smoke: an expired CO alarm chirps reassuringly on the test button while its sensor has quietly retired.
Gas Safety
What should tenants be told?
Three things, in writing: test the alarms regularly and report faults immediately; never remove batteries or units; and know the symptoms and response — headaches, drowsiness or nausea that lift outside the property mean fresh air first, then the gas emergency line, then the landlord. A short note at check-in covers all three and evidences the advice was given.
The advice is also a control in the legal sense: alarm regimes lean on tenant reporting to trigger the landlord's repair duty, so a tenant who knows what to report is part of the compliance system, not an audience for it.
Gas Safety
What does the evidence file look like?
The alarm schedule (type, location, expiry per unit), tenancy-start test evidence — dated inventory photographs remain the gold standard in England — fault reports and the dated repair or replacement that answered them, and the check-in advice note. Filed with the gas records, because any CO incident will summon both files at once.
It's a thin file guarding against a heavy event: after any suspected CO incident, the questions are exactly these — was the appliance checked, was the alarm present and in date, was the tenant told what to do. Three yeses, evidenced, is the entire defence and, better, the reason the incident stayed hypothetical.
Need the certificate itself?
The Smoke & CO Alarm Check page covers cost, process and every UK area we serve.
FAQ
Related questions, answered
Are alarm standards higher for HMOs in your area?
Usually — HMO licensing from your local council commonly specifies mains-powered, interlinked systems with heat detection in kitchens, at a higher grade than single-let minimums. Your licence conditions and fire risk assessment define the specification.
What are the tenant's responsibilities for alarms?
Routine testing during the tenancy, not removing batteries or units, and reporting faults promptly. The landlord's duty to repair or replace is triggered when the fault is reported.
Where should alarms be positioned?
Smoke alarms on ceilings in circulation spaces such as hallways and landings on each storey; CO alarms at head height in rooms containing the appliance, following the manufacturer's siting instructions. Avoid dead corners and locations right next to kitchens or bathrooms where nuisance triggering is likely.
Battery or mains-powered alarms — which do I need?
England's regulations don't mandate the power type for existing rentals, though sealed long-life batteries or mains power are recommended. Scotland requires sealed long-life battery or mains interlinked alarms; Wales requires mains-powered interlinked smoke alarms in rentals. Building regulations set standards for new work.
What does a smoke and CO alarm check involve?
Confirming the right alarms are present in the right locations for your nation's rules, that each one works when tested, that they are within service life, and documenting the result with dates and locations.
What are the alarm rules for rentals in England?
At least one smoke alarm on every storey used as living accommodation, and a carbon monoxide alarm in any room with a fixed combustion appliance other than a gas cooker. Alarms must be shown to work at the start of each tenancy, and landlords must repair or replace faulty alarms once informed.
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Ready to act on this? The pillar page covers the certificate end to end, with every UK area linked: Smoke & CO Alarm Check · Gas Safety Certificate (CP12).