What to Do If You Smell Gas or Suspect Carbon Monoxide

If you smell gas, the sequence is short and it matters: open doors and windows, turn the gas off at the meter using the emergency control valve unless the meter is in a cellar, touch no electrical switches, extinguish naked flames, leave the property and call the National Gas Emergency Service on 0800 111 999 from outside¹. The line is free and answered 24 hours a day¹. Northern Ireland uses a different number, 0800 002 001³.

The same number covers a suspected carbon monoxide release, which IGEM classes alongside a smell of gas and a gas escape as a gas emergency⁴. Carbon monoxide has no smell or taste, so it is not detected by nose at all; the alarm, the symptoms and the state of the flame are the signals⁵. If anyone is unwell, the priority shifts from the building to the people: fresh air first, then medical advice⁵.

What follows sets out the immediate steps, who attends and how quickly, what the emergency engineer will and will not do, the warning signs that precede an escape, and the annual servicing and registration checks that keep a household out of this situation. It also covers the landlord's gas safety record, which is a legal duty on rented homes and not on owner occupiers⁷.

Smell gas? Ventilate, shut the valve, touch nothing electrical

The actions are consistent across the network operators and the consumer bodies, and the order matters less than doing all of them. Open doors and windows to ventilate². Turn off the gas at the meter using the Emergency Control Valve, unless the meter is in a cellar or basement². Do not use electrical switches, do not smoke or use naked flames, and do not stay in a cellar or basement where gas is present¹.

The reason for the switch rule is blunt: turning a switch on or off could ignite a gas leak². That extends beyond light switches. Confused.com lists switches, doorbells and mobile phones among the electrical devices to avoid, and advises making the phone call from outside the property, particularly from a mobile¹². Gas itself is odourless, and a substance called mercaptan is added so that it can be detected at all¹².

The emergency control valve sits close to the meter. It is shut by turning the lever so that it is at 90 degrees to the gas pipe¹². Where the meter is in a cellar or basement and the smell comes from there, the advice is not to go down: the cellar should not be entered and the building should be evacuated instead¹².

For homes on bottled or tanked gas rather than mains, the procedure differs. Liquid Gas UK advises closing the manual outlet valve on the cylinder or tank, turning off all appliances and the property's emergency valve, opening doors and windows, not switching lights or electrical equipment on or off, calling the supplier, dialling 999 for the fire brigade and leaving the premises¹⁴.

Call 0800 111 999: free, 24 hours, and answered by an advisor

The National Gas Emergency Service is reached on 0800 111 999, a freephone number answered around the clock¹. Energy Networks Association gives the same number with the instruction to call immediately³. The service is free to call³. The Met Office repeats the number for gas emergencies, and HSE's guidance for householders carries it as the National Grid Gas Emergency freephone line¹⁶.

When the call connects, an advisor takes your details, gives advice on what to do and dispatches an emergency gas engineer². Northern Gas Networks describes the same flow: a trained advisor talks the caller through the steps, then arranges for an engineer to attend, carry out a full safety check, make the situation safe and provide safety advice¹⁷. SGN asks callers to disclose any vulnerabilities or special circumstances the advisors need to be aware of².

The engineer will carry identification and will need entry to the property to make it safe². Northern Gas Networks states its engineers arrive within one or two hours⁹.

Emergency numbers outside Great Britain

The 0800 111 999 line covers England, Wales and Scotland. Northern Ireland has its own number, 0800 002 001, given both by Energy Networks Association and in a government product safety report³. The Republic of Ireland uses 1850 20 50 50³.

The Isle of Man, Jersey and Guernsey are not covered by the numbers above in the material available here, and households there should confirm the local arrangement with their network operator or supplier. What is consistent is that the call is free and the response is treated as an emergency wherever it is made.

What the emergency engineer does on arrival

The engineer's job is to make the situation safe, not to repair. Northern Gas Networks states that its engineers do not repair appliances or pipework inside the home, but assess the situation, identify potential hazards and take the right action to make things safe in a gas emergency¹⁵. Cadent's description of the safety check is more detailed: the engineer checks that gas appliances burn correctly, are suitable for the room, physically stable, securely fitted and properly connected to the gas pipework, with adequate permanent air supply, functioning safety devices and correctly operating flues, chimneys and air vents¹⁹.

Where further work is needed, it falls to a separate visit. Northern Gas Networks advises that a Gas Safe Registered engineer may be needed to make further repairs to appliances or pipework⁹. Cadent says the same for extra work on ovens, boilers and fires¹³.

The practical consequence for a household is that the emergency visit ends with the property safe, not necessarily with the appliance working. A boiler or cooker isolated during the visit stays off until a registered engineer has attended to it. That is the point at which the household's dependence shifts from the network to a trade professional, and the choice of that professional is the household's own.

Suspected carbon monoxide: fresh air first, then medical advice

Carbon monoxide is a poisonous gas with no smell or taste⁵. The Northern Ireland guidance is more emphatic: it is a highly poisonous gas that cannot be seen, tasted or smelled, and it can kill quickly without warning²⁰. That is why the response differs from a gas escape. There is nothing to smell, so the alarm or the symptoms carry the warning.

If carbon monoxide is suspected in the property, the steps are to open all doors and windows, move everyone into the fresh air, and call the Gas Emergency Service on 0800 111 999²¹. Northern Ireland's guidance adds that anyone affected should stay outside in the fresh air, and that anyone who may have been exposed to carbon monoxide at levels suggesting symptoms should go immediately to a local emergency department⁵. HSE advises seeking urgent medical advice from either a GP or an A&E department where symptoms appear and exposure is suspected⁶.

The symptoms to watch for, per HSE, include headaches or dizziness, breathlessness, nausea, loss of consciousness, tiredness, pains in the chest or stomach, erratic behaviour and visual problems⁶. Liquid Gas UK lists headaches, nausea and dizziness when appliances are in use, and advises turning them off immediately¹⁴. Cadent notes that symptoms without any smell of gas could themselves be a sign of a carbon monoxide leak¹³.

Warning signs of a gas appliance problem

Long before an alarm sounds, appliances give physical signals. Cadent lists black marks and stains around the appliance, lazy orange or yellow flames instead of crisp blue ones, and high levels of condensation in the accommodation²³. SGN describes the same flame fault as burning a floppy yellow or orange rather than crisp and blue²⁴. A healthy flame should be crisp and blue²¹.

Other signs point to a leak rather than a combustion fault. Confused.com lists a weaker hob flame, hissing sounds from pipes or appliances, unexpectedly higher gas usage, dying plants and feeling unwell¹². It also notes that a gas stove giving off a tired-looking orange or yellow flame instead of the usual blue one is a tell-tale sign¹².

A pilot light that keeps going out belongs in the same list of appliance faults, though the material here does not give a UK figure for it. The pattern across all of these is that the appliance is telling the household something before the emergency number is needed. Acting on the sign, by switching the appliance off and arranging a service, is the step that keeps the household out of the emergency.

What the emergency service does not do

Two expectations need correcting. The first is that the emergency engineer will test the air for carbon monoxide or service the appliance. Northern Gas Networks states its engineers do not repair appliances or pipework inside the home¹⁵. The second is that the emergency visit resolves the appliance fault. It does not: further repairs require a Gas Safe Registered engineer¹³.

Where carbon monoxide is suspected, the official guidance points elsewhere for the investigation. The Northern Ireland guidance advises stopping use of all cooking and heating appliances, opening windows, seeing a doctor at once, and calling a qualified engineer to check all cooking and heating appliances²⁰. That is a separate appointment from the emergency call, and it is the one that establishes whether an appliance is the source.

The distinction matters for a household's energy independence. The emergency service is a network function, funded through the distribution networks and free at the point of call¹. The appliance work is a private transaction with a registered business. A household that has kept up annual servicing is far less likely to need either.

Prevention: annual servicing by a Gas Safe registered engineer

HSE strongly advises that all gas appliances, flues and pipework are installed, regularly maintained and serviced at least annually by a Gas Safe registered engineer⁷. Northern Gas Networks puts the same interval on boilers, cookers and water heaters²⁴, and SGN advises an annual check by a registered Gas Safe engineer for anyone with a gas boiler¹⁷. Liquid Gas UK advises annual servicing of gas boilers, gas cookers and gas water heaters²³.

The landlord's legal check runs on the same 12 month cycle. HSE states that a gas safety check must be done every year on each gas appliance and flue⁸, and that the annual check must be carried out within 12 months of the installation of the appliance⁷. Where a tenant prevents access, HSE inspectors look for at least three attempts to complete the check⁷.

The independence argument here is straightforward. A serviced appliance is less likely to produce the warning signs in the previous section, and a household that knows its engineer is registered is not exposed to illegal work. Gas Safe Register is the official register for gas engineers, and by law all gas engineers must be on it and hold current qualifications to install, repair or maintain domestic gas appliances²⁵.

Checking your engineer is Gas Safe registered

Every gas engineer carries a Gas Safe Register ID card, and every registered engineer should be able to show one, either as a hard copy or on a phone⁴. The card has two sides worth checking. On the front: the engineer's photograph, the start and expiry dates, the licence number, a security hologram, and confirmation that the engineer is from the business you contacted²⁰. On the back: the engineer's qualification to do the gas work you asked them to do, and confirmation that those qualifications are current²⁰.

The register itself can be checked in three ways. The Gas Safe website carries the register, and the helpline is 0800 408 5500¹⁰. A text check is available by texting Gas and the business registration number, or Gas and the engineer's seven digit licence number, to 85080⁷. Confused.com advises checking the Gas Safe website or asking to see the registration card if there is any doubt¹².

Gas Safe Register also handles finding a registered engineer, reporting illegal gas work undertaken by someone not registered, and complaints about unsatisfactory gas work⁴. For gas appliance and boiler problems, Cadent directs households to the register on 0800 408 5500¹¹. The registration requirement itself is enforced through the register: applicants must prove the necessary qualifications and experience to carry out gas work, and provide National Insurance numbers for any engineers they want to register²⁵.

Gas safety certificates and landlords: the CP12

The annual gas safety check and the record that follows it are a landlord duty, not a homeowner one. By law, landlords must carry out an annual safety check and provide the tenant with a Gas Safety Certificate³. The check must be done by a qualified Gas Safe engineer²⁸. Where there is a live gas supply to rented premises, a safety check must be carried out irrespective of whether the tenant uses gas⁷.

The record keeping is specific. The landlord must keep a record of the safety check for 2 years, issue a copy to each existing tenant within 28 days of the check being completed, and give a copy to any new tenant before they move in⁷. Tenants who rent and need a check arranged should contact the landlord to arrange a safety check for all gas appliances and flues by a Gas Safe registered engineer¹⁹.

Owner occupiers have no equivalent legal certificate. HSE's guidance for owner occupiers sits alongside the landlord duty and does not impose one¹⁰. The advice for owners is the servicing regime described above: an annual check by a registered engineer, on a voluntary basis, as a matter of safety rather than law.

There is no fixed price for a landlord gas safety record. Gas Safe Register states it has no control over engineers' charges and advises obtaining quotes from three different engineers before hiring⁷. Prices are installer-quoted. The HSE Gas Safety Advice Line, by contrast, is free and offers advice on gas safety⁷.

Where the household's independence ends

A gas supply is the one utility a household cannot make for itself. The emergency arrangements reflect that: the response is a network function, the number is free, and the engineer who attends comes from the local distribution network rather than from a business the household chose¹. What a household controls is everything on its own side of the meter: whether appliances are serviced annually, whether the engineer is registered, whether warning signs are acted on, and whether the emergency control valve can be reached without entering a cellar.

The dependence that remains is real and worth stating plainly. Until a registered engineer has attended, an appliance isolated during an emergency stays out of use. The household waits on a trade appointment, and on parts, and on the appliance's own condition. Annual servicing is the only lever that reduces the chance of reaching that point, and it is a legal duty only for landlords⁷. For everyone else it is advice, strongly given, from HSE and from every network operator in the country⁷.

For the wider picture of how a home's energy supplies are controlled and isolated, see how to turn off the gas, water and electricity in an emergency, and for the alarms that give early warning, how to test and maintain smoke, heat and carbon monoxide alarms. Households arranging the annual service itself will find the frequency question covered in how often should I have my boiler serviced?, and renters in who arranges a boiler service if you rent?.