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How does ACS renewal work for gas engineers?

ACS (Accredited Certification Scheme) qualifications must be reassessed every five years to keep your Gas Safe registration, covering CCN1 plus each appliance category you hold. There's usually a six-month window before expiry to reassess without a gap. Book at an ACS centre early: if your certificates lapse, you can't legally work on gas until you requalify.

Reviewed by Jordan Valentine-Dunn, Gas Safe registered engineer · Portsmouth Gas Heating · Last reviewed July 2026

ACS (the Accredited Certification Scheme) is how gas engineers prove ongoing competence. To keep your Gas Safe registration, your ACS qualifications must be reassessed every five years, covering CCN1 (the core) plus each appliance category you hold.

How the five-year reassessment works

Every category needs reassessing: CCN1 plus each appliance category, such as boilers, cookers and fires.
There's usually a six-month window before expiry to reassess without a gap in your qualifications.
Book at an ACS assessment centre well before your certificates lapse; centres get busy.
If your certificates expire, you cannot legally work on gas until you requalify.

ACS reassessment and Gas Safe renewal are not the same

It's easy to confuse the two. Your annual Gas Safe registration renewal is separate from the five-yearly ACS reassessment, and you need both to keep working legally. Diary the ACS expiry dates as carefully as the annual renewal, and check the current requirements with Gas Safe Register, as this is a general overview rather than formal guidance.

Frequently asked

How often do you have to renew ACS?

Every five years. Each ACS qualification you hold, CCN1 plus your appliance categories, must be reassessed on that five-year cycle to keep your Gas Safe registration valid.

Is there a grace period for ACS reassessment?

There's usually a six-month window before expiry in which you can reassess without a gap in your qualifications. Book early, because if your certificates lapse you cannot legally work on gas until you requalify.

Is ACS the same as my Gas Safe registration?

No. The two run on different cycles: Gas Safe registration renews annually, while ACS is reassessed every five years. You need both to work on gas legally, so it's worth tracking each set of dates separately.

Sources

Last reviewed July 2026. This guide is general information, not legal or safety advice, gas safety work must be carried out by an appropriately Gas Safe registered engineer. Rules can change, so check the linked official sources for the current position.

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