--- title: "CO Certification for Boiler Work | English Plumber Guide" description: "Booking a gas boiler installation or service? Learn what CO certification covers, where to check the company and which details to ask for before the visit." url: https://www.englishplumber.nl/guides/co-certificate/ language: en-NL alternate: https://www.englishplumber.nl/nl/advies/co-certificaat/ --- 1. [Home](https://www.englishplumber.nl/) 2. [Guides](https://www.englishplumber.nl/guides/) 3. CO certificate # How to check CO certification for boiler work If someone is working on your gas boiler, you should be able to check the certification behind the work. Here's where to look and what to ask before booking an installation, service or repair. Written by Jordan · Last checked 16 October 2026 - Check The responsible certified company - Register register.tlokb.nl - Applies to Covered gas appliance and flue work - Records Keep invoices and service details ## What is CO certification? Since 1 April 2023, companies carrying out covered work on gas combustion installations need a valid CO-vrij certificate. This includes gas boilers and related combustion-air and flue work. The certificate is held by the company, while the engineer also needs the relevant competence and identification. The [Toelatingsorganisatie Kwaliteitsborging Bouw](https://www.tlokb.nl/werkzaamheden-aan-gasverbrandingsinstallaties) explains the system and maintains the public register. [IPLO’s guidance](https://iplo.nl/regelgeving/regels-voor-activiteiten/gebruiken-bouwwerk/rijksregels/gasverbrandingsinstallaties/) explains the applicable building rules. ## How do I check the company? 1. Ask which certified company is responsible for the boiler work. 2. Find that company in the [official CO register](https://register.tlokb.nl/co/certificaathouder). 3. Check its current status and that the certification covers the intended work. 4. Ask the engineer to identify themselves when they arrive. 5. Keep the quote, invoice and service or commissioning records. A logo on a van or a personal training certificate is not a substitute for checking the responsible company. If the trading name and the certificate name differ, ask how they relate before work starts. ## Does it cover every plumbing job? The scheme concerns the gas combustion installation. A radiator replacement is a different kind of job, and gas pipework has its own requirements. When work also involves the boiler, air supply or flue, the scope needs to be considered properly. For an exact answer about a particular job, refer to the official guidance or ask the certified business to explain which requirements apply. ## What about an apartment with a shared flue? Tell the installer if your boiler is connected to a shared system. Ask the VvE or building manager for the flue information and inspection records. A replacement boiler and the shared system need to be suitable for each other before installation is agreed. ## What records should I keep? Keep the boiler details, invoice and maintenance records somewhere easy to find. Check the manufacturer’s maintenance instructions and warranty conditions for the model you have. Insurance terms also vary, so use your own policy or ask the insurer if you have a cover question. ## Booking with me English Plumber holds a CO-vrij certificate for all four kinds of work: installing, repairing, servicing and commissioning. The certificate number is SKGIKOB.018723.01.NL, issued by SKG-IKOB and valid until 1 October 2029. You can [check it in the CO register](https://register.tlokb.nl/co/certificaathouder/english-plumber-medemblik) yourself. You are welcome to ask about the certification and records for your job before booking. For a [new boiler](https://www.englishplumber.nl/services/boiler-installation/) or [service](https://www.englishplumber.nl/services/boiler-servicing/), start by [sending me photos, the model and your postcode](https://wa.me/31642869931). I’ll explain the work and the arrangements before we set a date. **Gas smell:** leave the property and call **0800 9009** from outside, avoiding flames and electrical switches. **CO alarm or suspected carbon monoxide poisoning:** get everyone outside and call **112**. Don’t wait for an appointment or a message back. ## More guides - [Servicing an ATAG boiler and reading its codes](https://www.englishplumber.nl/guides/atag-boiler/) - [Air in your underfloor heating, and how to get it out](https://www.englishplumber.nl/guides/bleeding-underfloor-heating/) - [Renting? Who looks after the cv-ketel](https://www.englishplumber.nl/guides/boiler-in-a-rented-home/) - [All guides](https://www.englishplumber.nl/guides/) ## Common questions Where can I check CO certification? Use the official public CO register at register.tlokb.nl. Check the company responsible for your job, its current status and the scope of its certificate. Is a personal training certificate enough? The company carrying out the covered work needs the relevant certification. Personal competence and company certification are separate checks. Should I ask before a boiler service? Yes. Check who is responsible for the certified work before booking, just as you would for a new installation. What should I keep after the job? Keep the quote, invoice, appliance details and service or commissioning records with the boiler documentation.