Short answer
Ask to see the engineer's Gas Safe ID card, check the business and engineer on the Gas Safe Register, and confirm the back of the card lists the non-domestic categories for the exact work — for example catering, boilers or testing and purging.
Step by step
Check the photo and licence number on the card, search the register online, and look for 'non-domestic' or 'commercial' against the relevant appliance type. Check expiry dates and ask for insurance details on larger jobs.
Red flags
Only domestic categories listed, refusal to show a card, no certificates offered at the end of the job, or vague answers about testing. Certificates such as CP16, CP17 or CP42 should carry the engineer's registration number.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
Need this done on site?
Need a commercial gas engineer in London?
Gas Safe registered commercial engineers, 24 hours a day. Call now or book online and we'll confirm a time.