Checked 21 October 2026. From IGEM's Standard Setting Body pages, Guidance Note 8 v8.1, CCN1 Issue 20.1 and HSE L56, read 21 Oct 2026. The number of questions, time allowed and pass rules are not published in these documents; ask your centre.
The ACS scheme's own documents say who sets the standard, who assesses you, and what kinds of evidence count. None of the documents quoted here publishes a question count, a time limit or a pass mark; ask your centre for the candidate information that applies to you.
Who is who in the scheme
| Role | Who | What it does |
|---|---|---|
| Law | Gas Safety (Installation and Use) Regulations 1998 (Great Britain) | Requires competence (reg. 3(1)) and membership of an HSE-approved class of persons (reg. 3(3)) |
| Approved class of persons | People registered with Gas Safe Register | HSE L56 para 102: "At the time of publication of this ACOP, the class of persons approved by HSE are those who are registered with Gas Safe Register" |
| Scheme owner and standards | Standard Setting Body, managed by IGEM | Its Strategic Management Board is "the Scheme Owner" of ACS and keeps the Matters of Gas Safety criteria |
| Certification body | Certification bodies; L56 says the schemes are operated by a certification body and accredited by UKAS (LCL Awards, for example, is No. 0230) | Issues your certificate of competence; your competence details reach Gas Safe electronically |
| Assessment centre | Centres listed in the ACS Gas Assessment Centre Directory (V16, Dec 2025) | Where you are assessed; IGEM links the directory for choosing a centre |
HSE's guidance in L56 describes the certification schemes in one sentence: they "require individual gas engineers to have their competence assessed at regular intervals under specific scheme arrangements set by the standards setting authority, operated by a certification body and currently accredited by the United Kingdom Accreditation Service (UKAS)." (L56, para 87.)
Our summary of the roles described by GSIUR, HSE L56, IGEM and Gas Safe Register, read 21 Oct 2026.
What is assessed: the Matters of Gas Safety
IGEM: "Before being accepted on the Gas Safe Register, engineers are required to demonstrate their competence in the type of work they wish to be registered for. Each work type has specific ‘Matters of Gas Safety’ that need to be demonstrated." For each type of work there is a core assessment and then appliance assessments. The criteria are grouped as Domestic, Meters and Emergency Response, LPG and Non-Domestic.
Inside a criteria document such as CCN1 the criteria come in two kinds, and each area has one or both (in CCN1, areas 1, 2 and 12 are knowledge only):
| Kind of criteria | What it means in the document | How it is shown |
|---|---|---|
| Performance criteria (PC) | Tasks and checks in the criteria, e.g. CCN1 area 5: "join copper tube using appropriate capillary end feed fittings, methods and agents" | Carried out and demonstrated at the centre; some items are marked OQ (oral questioning) |
| Knowledge and understanding (K&U) | What you must know, e.g. CCN1 area 2: "limits of flammability" | Answered; the CCN1 document lists "OQ. Oral questioning" for some items and does not say in what form the rest are asked |
HSE's definition explains why both are tested: "Competence is a combination of practical skill, training, knowledge and experience to carry out the job in hand safely, and ensuring the installation is left in a safe condition for use." (L56, para 85.)
Why the rigs at the centre can have faults built in
The Regulations treat an assessment centre differently from a customer's home. Regulation 2(8):
"These Regulations shall not apply in relation to a gas fitting used for the purpose of assessing the competence of a gas fitting operative at an assessment centre where such assessment is carried out for the purposes of a nationally accredited certification scheme, except that regulation 3(1) and (2) shall apply to work in relation to a gas fitting carried out by a person carrying out such assessment."
HSE's guidance gives the reason: these fittings "may have deliberate faults introduced, eg to demonstrate specific problems or test fault- detection techniques." So a fitting at a centre may be faulty on purpose.
Who can sit it: entry routes
IGEM: "New entrants into the gas industry are required to undertake an industry recognised training course before they are able to undergo assessments". The training standard is IGEM/IG/1. Guidance Note 8 (v8.1, implementation 1 October 2024) numbers 13 routes in three groups (route 5 is now left blank). Four examples:
| Group | Example | Training |
|---|---|---|
| Experienced gas engineer | Route 1: renewing an existing or expired ACS or GCS certificate | Optional |
| Experienced gas engineer | Route 3: holding a core ACS and extending range in the same sector | Required |
| New entrant with transferable skills or experience | Route 8: legal gas experience within GSIUR, wanting ACS in that sector | Managed Learning Programme (MLP) |
| New entrant without transferable skills or experience | Route 12: working to achieve a Category A or B core (CCN1 is Category A) | MLP |
GN8 defines an experienced engineer as one "registered or previously registered on GSR" who has held an ACS core or relevant qualification "for a minimum of 12 months". GN8 says Table 2 is it is "not intended to prevent or restrict movement but to ensure consistency"; ask your centre to confirm which route your evidence fits.
What HSE expects the training to cover
The assessment checks the result of training, so the training standard is worth knowing. HSE's Approved Code of Practice (L56, para 81) says gas work should only be undertaken "by a person who has successfully completed an industry- recognised training course followed by assessment of competence", or, "in the case of a currently or previously registered person," "where they have proved competence through a certification scheme". Para 82 adds that training should include "an adequate knowledge of: (a) relevant associated services such as water and electricity; (b) the potential for exposure to asbestos; (c) the dangers these may give rise to; (d) the precautions to take." Those are part of the training even though they are not gas fittings.
Core groups A, B and C
GN8 sorts the ACS core assessments into three groups, and its routes for changing sector differ by group (route 4 for Category A, route 10 for Category B, route 7 for Category C). From its Table 1:
| Group | Core assessments |
|---|---|
| A | CCN1, CCLP1-PD, CCLP1-RPH, COCN1, CCCN1, CCLNG1 |
| B | CESP1, CMA1, CMA3, CCLP1-EPC, CCLP1-LAV, CCLP1-B |
| C | COCNPI1LS, CMIT1, CMA2LS, CCLP1-MC, CCLP1-EP |
A Managed Learning Programme (MLP) is training approved by IGEM as the "Authoriser of Training" under IGEM/IG/1. For the MLP routes, GN8 limits two kinds of portfolio evidence (its Table 2 applies note 6 to routes 7, 8, 11 and 12, and note 5 to route 8; route 13 follows note 7 instead). Realistic Work Environment (RWE) evidence "must be obtained at an approved MLP training centre, be no greater than 10% of the portfolio content" and be recorded and identified as RWE, and a witnessed testimony (a signed declaration by the GSR engineer with whom the experience was gained) is evidence that must be "within the previous three years and amount to no greater than 50% of the portfolio content".
Try one question
How does regulation 26(2) allow a flued domestic gas appliance to be connected to the gas supply system?
- A. By a permanently fixed rigid pipe only
- B. By any flexible connector the manufacturer supplies
- C. By a bayonet fitting and hose, if it is easy to disconnect
- D. By whichever connection the customer prefers
Show the answer
A. Regulation 26(2): "No person shall connect a flued domestic gas appliance to the gas supply system except by a permanently fixed rigid pipe."
Our own question, written from the regulation quoted. It is not an ACS assessment question.
What we could not find, and will not guess
- The number of knowledge questions, the time allowed, and whether any paper is open book.
- A pass mark. The criteria documents list what must be demonstrated; they do not say how a result is decided.
- Assessment fees. The scheme documents quoted here do not state them; ask the centre for a quote.
Ask your centre for the certification body's candidate information before the day.
Frequently asked questions
Is the ACS gas assessment written or practical?
Both kinds of evidence are in the criteria: performance criteria you carry out and knowledge and understanding you answer, with each area using one or both. The CCN1 document lists oral questioning for some items. The form of the knowledge questions is not stated in the scheme documents; ask your centre.
Who sets the ACS criteria?
The Standard Setting Body managed by IGEM. Its Strategic Management Board is the Scheme Owner of ACS and maintains the Matters of Gas Safety criteria.
Who issues the ACS certificate?
A certification body; LCL Awards, for example, says it is UKAS accredited certification body No. 0230. Gas Safe Register receives the competence details electronically from the body.
Can I take ACS without training?
Not as a new entrant: IGEM says new entrants must complete an industry-recognised training course first. Experienced engineers renewing an existing certificate may take re-assessment without training.
What are the Matters of Gas Safety?
The assessment criteria for each type of gas work, kept by the Standard Setting Body. IGEM says each work type has specific Matters of Gas Safety that must be demonstrated, either within a qualification or through ACS.
Why do assessment rigs have faults?
Regulation 2(8) disapplies the Regulations for gas fittings used to assess competence at an assessment centre for a nationally accredited certification scheme, though regulation 3(1) and (2) still apply to the assessor's work. HSE guidance says such fittings may have deliberate faults introduced to test fault-detection.
ProSyllabus is an independent study site, not part of Gas Safe Register, HSE, IGEM or any ACS certification body. Rules here are quoted from the regulations and the scheme's own documents; ask your assessment centre how your own assessment will run.
Sources
- official — IGEM: The Role of the Standard Setting Body (SMB = Scheme Owner of ACS; read 21 Oct 2026)
- official — IGEM: Assessment, overview of Matters of Gas Safety, ACS and other routes to competence (read 21 Oct 2026)
- official — IGEM: Training for new entrants into the gas industry (IGEM/IG/1; read 21 Oct 2026)
- official — IGEM: ACS Entry Routes and Changeover Requirements, Guidance Note 8, version 8.1 (implementation 1 Oct 2024), linked from the Assessment page
- official — IGEM resource library: ACS.CCN1 Safety Assessment Criteria, Initial and Re-assessment, Domestic Natural Gas, Issue 20.1 (listed Oct 2026)
- official — HSE: L56 "Safety in the installation and use of gas systems and appliances", ACOP and guidance, fifth edition 2018 (paras 81, 85, 87, 102)
- official — legislation.gov.uk: Gas Safety (Installation and Use) Regulations 1998, regulation 2 (definition of "work"; 2(8) assessment centres)
- official — legislation.gov.uk: GSIUR 1998, regulation 26 (Gas appliances, safety precautions; 26(9)(ca) inserted 6 Apr 2018)
- official — LCL Awards (UKAS-accredited certification body No. 0230): What is the ACS Gas Scheme
- official — Energy & Utility Skills: ACS Gas Assessment Centre Directory, Version 16, December 2025 (linked from IGEM's Assessment page)
official = a document published by the conducting body. reported = a news or coaching site we could not check against an original. Where sources disagree this page says so rather than picking one.
