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How to check a gas leak

Updated: 20 October 2026

You can smell gas beside the cooker, or you have a handheld pen and you want to hold it on a joint before anyone is called out. How to check a gas leak in a UK home starts with that split. If you can already smell gas, you stop hunting and phone. A short-run sniffer is only a check at a joint when there is no smell and the reading stays quiet. The listings sit on the [gas detector](/hub/fire-protection/gas-detector) comparison. The Products Compared editorial team used National Gas, Cadent, SGN, the Health and Safety Executive, and Gas Safe’s emergency numbers, as checked on 20 October 2026. We did not run a detector or open a fitting. A qualifying purchase can earn a commission at no extra cost to you.

You can smell gas beside the cooker, or you have a handheld pen and you want to hold it on a joint before anyone is called out. How to check a gas leak in a UK home starts with that split.

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On this page
  1. 1.If you smell gas, stop checking
  2. 2.Northern Ireland and LPG use other numbers
  3. 3.What a sniffer is for
  4. 4.When you phone a Gas Safe registered engineer

If you smell gas, stop checking

If you smell gas, the check is the phone call, not a sweep along the pipe. National Gas gives 0800 111 999 for Great Britain, free and open 24 hours. Do not smoke or strike a match, and do not turn electrical switches on or off. Open doors and windows, turn the meter control off only if you know the handle and the meter is not in the cellar, and call from outside or from a neighbour’s house. The cellar is the case people reverse. National Gas says you do not turn the meter off when it is in the cellar, and SGN says you do not go down to reach the handle. Compared with a meter in the hall cupboard, which you can turn if you already know the control, a cellar meter is left alone and described on the phone. A strong smell on the stairs is already the call.

Northern Ireland and LPG use other numbers

Northern Ireland uses 0800 002 001 for natural gas, from Gas Safe’s emergency table. LPG uses the number on the vessel or its paperwork, not that line and not 0800 111 999. England, Scotland, and Wales stay on 0800 111 999, the number SGN and Cadent also publish. Walking the pipe while the room still smells delays the call, compared with phoning from the pavement. The emergency engineer makes the supply safe, and later appliance work is for a Gas Safe registered engineer.
TopTes TopTes PT520A

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TopTes TopTes PT520A
7.9/10about £39.99
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What a sniffer is for

A handheld gas sniffer is a short check at a joint you can see, and only when you do not already smell gas. The kind of pen in this category switches itself off after about five minutes. It is a check tool, not an overnight monitor, and not a reason to delay 0800 111 999 if a smell starts while you are holding it. Ventilate first, then hold the pen at the fitting. One tick is not a reading for the whole kitchen. A chirp on a cold union is a place to note, then stop. A carbon monoxide alarm does not see unburnt natural gas or LPG. If nobody smells gas and someone has a headache, feels sick, or is unusually tired, Cadent says those symptoms should ease in fresh air and names a GP visit, because that pattern can be carbon monoxide. The two devices are set out on gas detector vs carbon monoxide alarm. If the reading climbs while you stay on that nut, put the pen down and phone a Gas Safe registered engineer. Compared with a fixed alarm left on the wall, this pen is finished when it switches off, so a quiet pass on one joint is as far as it goes.

When you phone a Gas Safe registered engineer

Phone a Gas Safe registered engineer if you smell gas, if the reading climbs, before anyone undoes a fitting, before the supply goes back on, and if anyone feels dizzy or sick. The Health and Safety Executive says it is illegal to use an appliance you suspect is unsafe, so a hob you have switched off stays off until a registered engineer says otherwise. Tightening the nut because the pen reacted is still gas work. Under the Gas Safety (Installation and Use) Regulations 1998, disturbed pipework is followed by a tightness test and a purge, done by the person allowed to do the work. Leave the fitting untouched. Nothing here describes how to take a union apart. If you turned the meter off, and it was not in a cellar, do not turn it back on to test the smell. The emergency engineer makes the supply safe, and SGN says appliance work afterwards is for a Gas Safe registered engineer. A check of about five minutes is not that all-clear. Get a dizzy person into fresh air first. Cadent expects dizziness, fatigue, nausea, and headache to ease outside, and names a GP visit. If you can also smell gas, phone before any further sniff. The detector warns. It does not stop a leak, and it does not replace the emergency service or a Gas Safe registered engineer.

Common questions

What do I do first if I can smell gas?
Phone before you look for the joint. In Great Britain call 0800 111 999, free and open 24 hours. Do not smoke or light a match, and do not turn electrical switches on or off. Open doors and windows. Turn the meter off only if you know the control and it is not in the cellar, then call from outside. A sniffer does not come before that number.
Can I trace the leak with a sniffer before I phone?
Only when you cannot smell gas. A pen that switches off after about five minutes is a check at a visible joint, not a search you start because the kitchen already smells. If you can smell gas, 0800 111 999 comes first. If there is no smell and the reading climbs, stop and phone a Gas Safe registered engineer.
What is the number in Northern Ireland, and what about LPG?
Natural gas in Northern Ireland uses 0800 002 001 on Gas Safe’s emergency table, a different line from Great Britain. LPG uses the number printed on the vessel or on the papers with the cylinder or tank, not 0800 111 999 and not the Northern Ireland mains number. England, Scotland, and Wales stay on 0800 111 999 for a smell of mains gas.
Why must I not turn light switches on or off?
National Gas places electrical switches in the same list as matches and smoking, so you leave the light and the extractor as you found them while you can smell gas. Open the doors and windows, and call from outside. With no smell, a short check at a quiet joint is not that emergency sequence.
Can I tighten a joint if the pen reacts?
No. A reaction on the pen is a stop, not a cue for a spanner. Tightening a gas fitting is gas work, and the Gas Safety (Installation and Use) Regulations 1998 require a tightness test and a purge after pipework is disturbed. That is for a Gas Safe registered engineer. Leave the nut as it is and phone.
What if someone feels dizzy?
Get them into fresh air before you touch the joint. Cadent lists dizziness, fatigue, nausea, and headache, and says those symptoms should ease outside. A GP visit is the precaution they name. If you can also smell gas, call 0800 111 999 in Great Britain, or 0800 002 001 for natural gas in Northern Ireland. Do not stay inside to finish a sniff.

Related pages

Natural gas or LPG detector

Gas detector buying guide

Gas detector

Best gas detector for a joint or the leave-on alarm

Gas detector vs carbon monoxide alarm, two hazards

Sources

Safety rules and standards are from the public sources below. Prices, stars, and review counts are from the amazon.co.uk listings. Last checked 20 October 2026.

  1. National Gas emergency contacts (retrieved 20 October 2026)
  2. HSE domestic gas FAQs (retrieved 20 October 2026)
  3. Gas Safety (Installation and Use) Regulations 1998 (retrieved 20 October 2026)
  4. HSE L56, safety in the installation and use of gas systems and appliances (retrieved 20 October 2026)
  5. GOV.UK smoke and carbon monoxide alarm booklet for landlords (retrieved 20 October 2026)
  6. BSI BS EN 50194-1:2023, flammable gases in household premises (retrieved 20 October 2026)
  7. Cadent, sense of smell (retrieved 20 October 2026)
  8. Safelincs: will a carbon monoxide alarm detect gas leaks? (retrieved 20 October 2026)