ACS CCN1 2026: Free Guide to the Core Gas Assessment

CCN1 in 2026: What It Is, and the Two Things That Changed

ACS CCN1 (Core Domestic Natural Gas Safety) is the core certificate of competence you must hold to be Gas Safe registered for domestic natural gas work in Great Britain — but on its own it will not get you registered, and two industry standards behind it change during 2026.

That is the part most CCN1 pages leave out. CCN1 is not a standalone licence; it is one half of a pairing — the core assessment plus at least one appliance category. And if you are sitting or re-sitting CCN1 in the second half of 2026, the correct answer to two familiar exam topics, tightness testing and unsafe-situation classification, is not what older revision material says it is.

This guide covers the route in, the assessment format, the 2026 standards changes, the timing cliffs on reassessment, real costs, and where candidates lose marks.

free ACS CCN1 practice questionsPractice questions with detailed explanations

---

CCN1 Snapshot (2026)

The scheme runs through UKAS-accredited certification bodies and their approved centres — LCL Awards, BPEC, NICEIC and others — so assessment content is consistent nationally, but pricing and timetabling are not.

---

The Registration Equation: CCN1 Is Half the Answer

You cannot join the Gas Safe Register with CCN1 alone. The register issues you an ID card showing the categories of gas work you are qualified to do, and CCN1 by itself buys you almost nothing practical — gas installation pipework and not much else. To do useful domestic work you pair CCN1 with one or more appliance categories:

Most new engineers take CCN1 + CENWAT as the minimum viable combination, then add CKR1 and HTR1.

Two points that catch people out. First, CPA1 (combustion performance analysis) is already contained inside CCN1. Since April 2012, candidates sitting CCN1 have not needed a separate CPA1 certificate; it survives as a standalone assessment only for people whose core qualification sits elsewhere. Second, adding appliance categories later is harder than adding them at the same time. Centres advise that you must have held Gas Safe registration for a minimum period — 12 months under the rule introduced in September 2022 — before adding categories that were not part of your original assessment. Take the appliances you need in the same booking if your portfolio evidence supports it, because retrofitting them is a year-long wait, not a phone call.

---

Which Route Are You On? Categories 1, 2 and 3

Before you can book CCN1, the centre has to place you in an ACS candidate category. This is the gate most guides skip entirely, and it decides whether you can sit the assessment next month or next year.

• Category 1 — experienced practising gas fitting operative. You already work in gas. Straight to assessment; refresher training optional.
• Category 2 — holds qualifications listed in ACS Guidance Note 8 (or GN8a for gas experience gained outside the scope of GSIUR, e.g. Armed Forces or overseas work). You must give the centre written evidence: a statement from a registered business detailing the type, range and volume of gas work you have carried out, plus a certificate or statement from your training provider.
• Category 3 — new entrant. Anyone who does not satisfy Category 1 or 2. You must complete a Managed Learning Programme (MLP) before you are eligible to sit ACS.

The MLP route for new entrants

The MLP is built to IGEM/IG/1 Edition 2 and its supplements (Supplement 2 covers the domestic natural gas training specification). It is not a short course. It combines classroom and workshop training with a portfolio of real, verified on-site gas jobs completed under the supervision of a Gas Safe registered engineer — and that portfolio is what unlocks your ACS booking, not the classroom time.

A typical part-time programme runs around 45 weeks: roughly 25 weeks of training, an 18-week supervised placement to build the portfolio, then about a week of ACS assessment. Intensive variants compress this, but the portfolio cannot be skipped. Providers quote £7,000–£8,000 including VAT for a full programme — Skills Training Group publishes £7,770 — so the CCN1 assessment fee is a small slice of a much larger number.

When you apply for ACS certification, Gas Safe Register expects evidence of the qualification, the name, address and registration number of the business that supervised your training, the start and end dates of on- and off-the-job training, and the types and sufficiency of gas work you undertook.

---

What the Assessment Actually Looks Like

CCN1 is open book. You may reference British Standards, IGEM standards and technical bulletins during the written papers, and the assessment draws on material from more than 20 British Standards plus supporting legislation. That sounds generous. In practice it is why candidates fail: open book rewards people who can find a value in 40 seconds, and punishes people who planned to look everything up.

Assessment uses "a variety of assessment methods including multiple choice, short written response and scenario questions and observed practical assessment" (LCL Awards). Some subject areas are written-only; most carry both a written and an observed practical component:

Every subject area must be passed. There is no compensating a weak area with a strong one, which is why "I'm good at the practical" is not a strategy. Initial assessment typically runs three to five days at a centre; reassessment is usually two days.

---

The Two 2026 Changes That Alter Your Answers

This is the part no training-centre sales page will tell you, because it does not sell a course.

1. IGEM/UP/1B Edition 4 — tightness testing changes on 1 October 2026

IGEM/UP/1B Edition 4 was published in March 2026, takes effect on 1 October 2026, and Edition 3 is withdrawn on 30 September 2026.

The substantive change matters for CCN1: under Edition 3 you assessed a tightness test against meter-based tables (U6, U16 and so on). Under Edition 4, permissible pressure drops are dictated by the Installation Volume (IV), not just the meter size. The scope covers an installation volume supplying an individual dwelling or non-domestic premises not exceeding 0.035 m³, with a meter badged capacity not exceeding 16 m³/h and MOP at the emergency control valve outlet not exceeding 2 bar for natural gas.

Practically: if your assessment date is on or after 1 October 2026, revise the tightness test as an installation-volume calculation, not a table lookup. If it is before that date, Edition 3 still applies — but any material printed before March 2026 will be silent on the change, so check which edition your centre is assessing against when you book. Confirm the current position on IGEM's standards page.

2. GIUSP has no "NCS" — and has not for years

A large amount of CCN1 revision material still teaches three unsafe-situation classifications: Immediately Dangerous (ID), At Risk (AR) and Not to Current Standards (NCS). That is out of date.

The current procedure is IGEM/G/11 Edition 2 with amendments July 2022, June 2024 and July 2025 (Communication 1904). It defines two categories — ID and AR — and applies them using GSIUR 1998 and the HSE Approved Code of Practice L56. The term NCS does not appear in the document at all.

NCS was removed from the procedure in July 2016, on the reasoning that something not to current standards is, by definition, not unsafe, and therefore has no place in an unsafe situations procedure. It was not banned as a concept — you may still tell a customer their installation does not meet current standards — but per Gas Safe Register guidance it should not be recorded on warning notices or safety-related paperwork. Critically, an NCS-type situation is not At Risk; do not upgrade it.

If a scenario question asks you to classify a situation, your available answers are ID or AR. You can read the full current procedure in the GIUSP PDF hosted by Gas Safe Register.

Also worth checking: BS 5440-1:2023 and BS 5440-2:2023 replaced the 2009 editions with effect from 31 December 2023. BS 5440-2:2023 was aligned with Approved Documents F1 and F2, restricts air vents passing through fire-rated compartments, and renumbered several tables (old Table 6 is now Table 4). If you are working from a pre-2024 manual, your table references will not match the book on the desk in front of you.

---

Initial vs Reassessment: Two Timing Cliffs

ACS certificates last five years. Two dates decide which assessment you sit.

• Up to 6 months before expiry — reassess early and keep your full five years from the original expiry date. Nothing is lost, so there is no reason to leave it late. Gas Safe Register treats evidence of competence as unacceptable once it is five years old, so a lapsed certificate means suspension, not a grace period.
• More than 12 months after expiry — reassessment is no longer available. You must sit the initial assessment again: longer, more expensive, and for a Category 3 candidate potentially back through training.

Between expiry and the 12-month mark you can still reassess, but you cannot legally work on gas in the gap. Reassessment also only covers modules you previously held — you cannot acquire a new appliance category through a reassessment booking.

---

What CCN1 Costs in 2026

Two separate bills: the assessment, and the registration.

ACS assessment (centre-set, varies widely). Published 2026 examples: a two-day CCN1 reassessment from about £310; a CCN1 + appliances reassessment package around £965; a five-day initial package around £936 including VAT. New entrants should budget for the full MLP instead.

Gas Safe registration (official, 1 April 2026 – 31 March 2027):

A brand-new business therefore pays £319.96 plus VAT (£383.95 inc VAT) — application fee plus new registration fee. Registration runs 12 months and must be renewed annually, with web renewal the cheapest route. Figures come from the Gas Safe Register fees page; several third-party guides still quote the pre-April-2026 total.

After you register: you get three months of probationary status. You are fully registered and can work, but you must notify all completed gas work and keep records, and Gas Safe Register will inspect. Fail to provide evidence of gas work and the business is suspended; probation can be extended if inspected work is not up to standard.

---

Where Candidates Actually Lose Marks

• Treating open book as a substitute for knowledge. Tab your GSIUR, BS 5440-1/-2, IGEM/UP/1B and GIUSP before you sit down, and practise locating values against a clock.
• Revising from superseded material. ID/AR/NCS, pre-2023 BS 5440 tables, and Edition 3 tightness testing after October 2026 are all confidently wrong answers.
• Under-preparing the written-only areas. Legislation, gas characteristics, pipework sizing and fluing standards carry no practical, so nothing hands-on can rescue a weak paper.
• Missing one subject area. Every area must be passed independently.
• Booking without portfolio evidence. Category 3 candidates who arrive with an incomplete portfolio do not sit.
• Forgetting the appliance module. Passing CCN1 and then discovering you cannot register is a common and expensive mistake.

---

A Four-Week CCN1 Prep Plan

Week 1 — Legislation and emergencies. GSIUR 1998 duties, landlord duties under Regulation 36, the emergency control valve, gas escape procedure and RIDDOR reporting. Read the current GIUSP end to end so ID and AR are automatic.

Week 2 — Gas characteristics, tightness testing and rating. Gas properties, calorific value, gas rating and heat input, standing and working pressure. Learn the tightness test to the edition you will be assessed against, and know how to compute installation volume.

Week 3 — Pipework, ventilation and flueing. Pipe sizing and permissible pressure drop, sleeving and bonding, BS 5440-2:2023 ventilation, flue types, flue flow and spillage testing, terminal siting under BS 5440-1:2023.

Week 4 — Combustion, controls and full practice runs. Flue gas analysis and CO/CO₂ ratio interpretation, controls and safety devices, commissioning. Then run mixed question sets under time and review every miss against the source standard, not a memorised answer.

---

Free CCN1 Prep on OpenExamPrep

• ACS CCN1 practice questions — 100+ questions with worked explanations across all core subject areas
• CCN1 study guide — structured review of the core syllabus
• CCN1 flashcards — for the values you must recall instantly
• CCN1 cheat sheet — dense final-week reference

CENWATPractice questions with detailed explanations

---

Official Sources

• Gas Safe Register — Path to Gas Safe registration
• Gas Safe Register — Registration fees (2026–27)
• IGEM/G/11 Edition 2 with amendments July 2022, June 2024 and July 2025 (GIUSP)
• IGEM — All technical gas standards (UP/1B Edition 4, IG/1 Edition 2)
• LCL Awards — ACS Core Domestic Natural Gas Safety and Appliances
• IGEM — Standard Setting Body for the gas utilisation industry

---

Key Takeaways

1. CCN1 plus at least one appliance category is the minimum for Gas Safe registration — CCN1 alone is not enough.
2. CPA1 is already inside CCN1; you do not need it separately.
3. Your ACS candidate category (1, 2 or 3) decides whether you can book now or need an MLP and portfolio first.
4. IGEM/UP/1B Edition 4 takes effect 1 October 2026 and bases permissible tightness-test pressure drops on installation volume, not meter size.
5. The current GIUSP has only ID and AR — NCS was removed in July 2016 and must not appear on warning notices.
6. Reassess up to 6 months early to keep your full five years; more than 12 months lapsed means starting over with an initial assessment.
7. Budget the assessment fee and the Gas Safe registration fee separately — £319.96 plus VAT to join the register in 2026–27.