CO alarm check vs official CO inspection: the difference

A customer calls: "We've got a CO alarm on the wall, so we're fine, right?" That's exactly the confusion this article is about — and that confusion can cost an installation company dearly if a customer thinks that a beeping box on the ceiling is the same thing as a legally required, certified check of the central heating installation.

A CO alarm check and an official CO inspection are two completely different things, with a different legal status, a different purpose and a different person carrying it out. In the checklist for a CO inspection we already go deep into how you carry out and record that formal inspection yourself — this article focuses on the distinction, so that you can communicate it clearly to customers.

What is a CO alarm check?

A CO alarm (carbon monoxide alarm) is a consumer device that sounds an alarm as soon as a dangerous concentration of carbon monoxide is present in the room. It is comparable to a smoke alarm, but for a gas you cannot smell, see or taste.

Important to know:

• A CO alarm in a home is not legally required in the Netherlands, but is widely recommended — among others by the Rijksoverheid and the fire brigade — precisely because carbon monoxide is released unnoticed.
• A "check" of a CO alarm is nothing more than checking whether the device works: battery, test button, possibly the sensor's expiry date. The customer can do that themselves, or a technician checks it briefly during a maintenance visit.
• A working CO alarm says nothing about the condition of the central heating boiler, the flue gas discharge or the combustion air. It is a reactive measure — it only warns once carbon monoxide is already being released.

What is an official CO inspection?

A CO inspection is a preventive, certified check of the gas combustion installation itself: the central heating boiler, gas water heater, gas fire or collective flue gas discharge system (CLV). This is the domain of the Gasketelwet, as explained in what is the Gasketelwet.

Key points:

• Since 1 April 2023 this work may only be carried out by companies and technicians with a valid CO certificate (Bewijs van Vakmanschap CO) — see the CO-person certificate.
• The inspection takes place under a recognised assessment guideline: BRL 6000-25 (InstallQ, certified by Kiwa/Normec/Bureau Veritas/Dekra), BRL K25000 (Kiwa) or BRL SI-6025 (CO-Keur, aimed at smaller companies without CLV work). Which guideline a certifying body applies differs per organisation — for the customer that makes little practical difference, as long as the company is certified.
• It is carried out using calibrated measuring equipment and a standardised checklist, not by pressing a test button.
• The technician assesses, among other things, the combustion, the flue gas discharge and the combustion air supply — exactly the things a CO alarm cannot see.

The core of the difference

• CO alarm check: testing the device, no certificate required, reactive (warns once something has already gone wrong), not legally required for the owner.
• CO inspection: inspecting the installation itself, only by a CO-certified company, preventive (identifies risks before something goes wrong), linked to the Gasketelwet obligations for building-related gas combustion appliances.
• An approved CO alarm is therefore not a substitute for a CO inspection, and conversely a CO inspection does not replace the recommendation to install a CO alarm — they complement each other, but are not synonymous.

Why this confusion is a risk for your business

If a customer thinks the CO alarm is "enough", they may unjustifiably postpone a CO inspection — with a safety risk for the occupants and a reputational risk for your business if something goes wrong later. Conversely: if, as a technician, you only briefly test the CO alarm during a maintenance visit, but don't clearly distinguish this on the work order from a full CO inspection, that can be misinterpreted in a dispute or an audit.

So be explicit in your communication and on the work order: state literally whether you tested a CO alarm, carried out a CO inspection, or both, that day. See what needs to be on a work order for the broader requirements for a correct work order.

Reporting obligation for a dangerous CO value

If during an inspection you measure a CO concentration that exceeds the limit value in a space where people can be present, a reporting obligation applies: the installer must report this to the occupant/user and owner of the building, the competent authority and the certifying body. This follows from the regulations around gas combustion installations (Bbl/Omgevingsregeling). Because the exact wording and threshold value in legal texts can be updated, we recommend checking the current text with IPLO or wetten.overheid.nl before communicating this to customers as a fixed standard.

How often must a CO inspection take place?

Here sources diverge and caution is warranted: there is no unambiguous, legally established fixed retesting interval for every situation. For the nuance and the practical approach we take, see CO inspection: why there is no fixed retesting interval laid down. So avoid presenting a hard, general interval ("every 2 years" or "every year") to customers as a legal obligation without verifying this locally — instead, advise on the basis of the appliance, the installation and the advice of the manufacturer or certifying body.

In practice: what can you do as a company?

• Explain the difference clearly in customer communication (quote, work order, website) — don't use "CO check", "CO test" and "CO inspection" loosely interchangeably as if they were the same thing.
• Always recommend a CO alarm as a supplement, never as a replacement for a CO inspection.
• Make sure only CO-certified technicians carry out the formal inspection, and sign the work order with the correct certificate number.
• If in doubt about a measured value: follow the reporting obligation and document this explicitly, instead of dismissing it as "well, the CO alarm didn't go off anyway".