Gas words
Gas safety words, in plain English
Engineers' paperwork and landlord rules use a lot of shorthand. Here are the terms you're most likely to meet, each in a sentence.
Short answer
The terms that matter most: the Gas Safe Register and its categories of work, the gas safety record (often called a CP12), fixed combustion appliance, and the gas emergency number, 0800 111 999.
- At risk / immediately dangerous
- Classifications an engineer gives an unsafe appliance; both carry a "Danger, Do Not Use" label.
- Balanced flue
- A flue that draws air from and vents fumes directly outside, sealed from the room.
- Bayonet fitting
- A push-in connection for a free-standing cooker’s flexible hose. More
- Carbon monoxide (CO)
- A colourless, odourless poisonous gas produced when fuel burns badly. More
- Categories of work
- The types of gas work an engineer is registered for, shown on the back of the ID card. More
- CP12
- An old name, still widely used, for a landlord’s gas safety record. More
- Fixed combustion appliance
- An appliance that burns fuel and is fixed in place, such as a boiler, gas fire or wood-burner; gas cookers are excluded from the CO alarm rules.
- Flue
- The pipe or chimney that carries combustion products out of the home. More
- Gas emergency number
- 0800 111 999, for a smell of gas or suspected leak. More
- Gas Safe Register
- The official list of businesses and engineers competent to do gas work, operating under an agreement with HSE.
- Gas safety check
- A landlord’s legally required annual safety inspection of appliances and flues. More
- Gas safety record
- The document recording a gas safety check, which tenants must receive.
- GSIUR
- The Gas Safety (Installation and Use) Regulations 1998.
- HSE
- The Health and Safety Executive, which oversees gas safety in Great Britain.
- LGSR1
- HSE’s form for tenants to report a missing gas safety record. More
- LPG
- Liquefied petroleum gas, from a tank or bottles.
- Meter control valve
- The lever near the gas meter that turns off the supply.
- Open flue
- A flue arrangement that takes combustion air from the room, so ventilation matters.
- Service
- Maintenance of an appliance; HSE advises at least annually. More
- Boiler Upgrade Scheme
- A grant towards heat pumps and biomass boilers, not gas boilers. More
Where the definitions come from
The terms follow HSE's wording in its domestic gas FAQs and guidance for landlords, and GOV.UK's guidance on carbon monoxide alarms, read on 3 November 2026. The full list is on our sources page.
A question about gas work in your home?
Tell us what you're trying to sort out. Your message reaches SEO-DONS LTD, the publisher of this guide, and we answer by email. We don't do gas work or recommend engineers, but we can tell you what to check and where. If you smell gas, don't write to us: call 0800 111 999 now.
What happens next
- Your message reaches SEO-DONS LTD, which publishes this guide.
- We reply by email with the rule or check that applies.
- Any work is between you and a Gas Safe registered engineer you choose.