About the exam
ACS CCN1 Gas Core Exam structure
An independent study guide aligned to the IGEM Standard Setting Body CCN1 Issue 19 criteria for initial and reassessment of core domestic natural-gas safety competence.
Issuer and path
ACS CCN1 Core Domestic Gas Safety Study Guide is administered through UKAS-accredited ACS certification bodies. Check official resources before booking, retesting, or relying on a stale requirement.
1. Gas Safety Legislation and Standards
0 scored + 0 pretest
Legal duties, competence, registration, standards, regional requirements, records and reporting relevant to domestic natural-gas work.
2. Gas Emergencies, Actions and Procedures
0 scored + 0 pretest
Immediate actions, isolation, ventilation, ignition control, escalation and advice when gas is suspected or confirmed.
3. Products and Characteristics of Combustion
0 scored + 0 pretest
Complete and incomplete combustion, carbon monoxide risk, analyser use and combustion-performance decisions.
4. Ventilation
0 scored + 0 pretest
Ventilation purpose, free-area calculations, provision, location, interaction and practical verification.
5. Installation of Pipework and Fittings
0 scored + 0 pretest
Domestic pipework materials, sizing, routing, support, jointing, protection, bonding and inspection.
6. Tightness Testing and Purging
0 scored + 0 pretest
Let-by, stabilisation, tightness testing, leak response, purging and recording within the current CCN1 installation scope.
7. Checking Operating Pressure at Outlet of Meter
0 scored + 0 pretest
Safe measurement, interpretation and escalation of operating pressure at the meter outlet.
8. Unsafe Situations, Emergency Notices and Warning Labels
0 scored + 0 pretest
GIUSP-based identification and classification, immediate action, notices, labels, records and reporting.
9. Operation and Positioning of Emergency Isolation Controls and Valves
0 scored + 0 pretest
Operation, accessibility and acceptable positioning of ECVs, AECVs and MIVs.
10. Checking and/or Setting Appliance Burner Pressures and Gas Rates
0 scored + 0 pretest
Manufacturer-led burner-pressure and gas-rate checks, calculations, tolerances and corrective decisions.
11. Operation and Checking of Appliance Gas Safety Devices and Controls
0 scored + 0 pretest
Operation, checking, permitted intervention and restoration of domestic appliance gas safety devices and controls.
12. Chimney Standards
0 scored + 0 pretest
Selection, construction, route, termination, supports, air supply and regional requirements for chimney systems.
13. Chimney Inspection and Testing
0 scored + 0 pretest
Visual inspection, flue-flow and spillage testing, room-sealed checks and evidence-led decisions.
14. The Installation of Open, Balanced and Fan-Assisted Chimneys
0 scored + 0 pretest
Safe assembly, connection, support, termination and inspection of common domestic chimney arrangements.
15. Re-establishing the Gas Supply to the Gas Installation and Relighting Appliances
0 scored + 0 pretest
Controlled restoration, purging, relighting, post-work checks, user information and treatment of uncommissioned appliances.
16. Inspecting, Testing, Commissioning and Maintenance of Gas Appliances (Reassessment Only)
0 scored + 0 pretest
The appliance-work category included by the current CCN1 criteria for reassessment candidates only.
Before you book or rely on a remembered rule
Confirm the current ACS entry route, assessment combination, approved documents, equipment and reassessment timing with your chosen certification body or assessment centre. For real work, check the nation, business registration and operative work categories.
Official Outline Coverage Map
Coverage is mapped to official outline item counts so content depth can be checked without hard-coding a single exam.
| Topic | Official outline items | Your questions | Your flashcards | Confidence |
|---|---|---|---|---|
| Gas Safety Legislation and Standards | 0 | 45 | 6 | Strong |
| Gas Emergencies, Actions and Procedures | 0 | 35 | 6 | Strong |
| Products and Characteristics of Combustion | 0 | 55 | 6 | Strong |
| Ventilation | 0 | 40 | 6 | Strong |
| Installation of Pipework and Fittings | 0 | 55 | 6 | Strong |
| Tightness Testing and Purging | 0 | 55 | 6 | Strong |
| Checking Operating Pressure at Outlet of Meter | 0 | 25 | 6 | Strong |
| Unsafe Situations, Emergency Notices and Warning Labels | 0 | 45 | 6 | Strong |
| Operation and Positioning of Emergency Isolation Controls and Valves | 0 | 20 | 6 | Strong |
| Checking and/or Setting Appliance Burner Pressures and Gas Rates | 0 | 30 | 6 | Strong |
| Operation and Checking of Appliance Gas Safety Devices and Controls | 0 | 40 | 6 | Strong |
| Chimney Standards | 0 | 35 | 6 | Strong |
| Chimney Inspection and Testing | 0 | 40 | 6 | Strong |
| The Installation of Open, Balanced and Fan-Assisted Chimneys | 0 | 30 | 6 | Strong |
| Re-establishing the Gas Supply to the Gas Installation and Relighting Appliances | 0 | 30 | 6 | Strong |
| Inspecting, Testing, Commissioning and Maintenance of Gas Appliances (Reassessment Only) | 0 | 21 | 6 | Strong |
How to use this guide
How to prepare for CCN1 safely
Build a source-led decision sequence, practise calculations and document navigation, and rehearse every practical task with an approved centre or competent trainer.
1. Establish jurisdiction and scope
Identify the UK nation, premises, fuel, pressure, installation type, appliance category, task and the operative's permitted scope.
2. Control immediate danger
Stop unsafe work, remove ignition risk, isolate when safe, ventilate or evacuate as required and contact the emergency service provider when the situation crosses that boundary.
3. Select the controlling source
Use current legislation, GIUSP, standards, assessment documents and manufacturer's instructions for the exact installation and task.
4. Inspect, measure and calculate
Prepare suitable instruments, establish required conditions, work in visible units and record enough evidence to reproduce the decision.
5. Compare and act
Compare evidence with the applicable criterion, then rectify within competence or classify, isolate, notify and refer through the prescribed route.
6. Restore and hand back
Prove tightness, purge, relight eligible appliances, complete affected safety checks, explain final status and retain the required record.
Current official structure
All 16 CCN1 competence categories
The study structure mirrors Issue 19 without inventing national question weights or collapsing the reassessment-only category.
Legislation, Competence and Standards
How statutory duties, Gas Safe registration, ACS competence, current standards and regional rules control gas work.
Choose a topic to open below
Gas Emergency Response
A safe priority sequence for suspected escapes, continuing gas flow and occupier or emergency-service advice.
Choose a topic to open below
Combustion and Carbon Monoxide
Combustion science, appliance evidence, analyser discipline and proportionate action on unsafe results.
Choose a topic to open below
Ventilation Provision and Interaction
Ventilation requirements, calculations, inspection and the effect of compartments, extractors and draught proofing.
Choose a topic to open below
Domestic Pipework and Fittings
Material selection, sizing, routes, joints, support, protection and practical quality controls for domestic pipework.
Choose a topic to open below
Tightness Testing and Purging
The current procedure and decision points for let-by, stabilisation, testing, leak response, purge and records.
Choose a topic to open below
Meter Outlet Operating Pressure
Accurate measurement and the correct response when the meter-outlet operating pressure is outside the applicable range.
Choose a topic to open below
Unsafe Situations Procedure
Evidence-led GIUSP classification, immediate controls, communication, labels, records and statutory reporting awareness.
Choose a topic to open below
Emergency and Appliance Isolation
Safe use and positioning of the valves that isolate a premises, installation branch or appliance.
Choose a topic to open below
Burner Pressure, Heat Input and Gas Rate
Instrument setup, manufacturer data, rate calculations and interpretation without unsafe adjustment.
Choose a topic to open below
Safety Devices and Controls
Functions, checks, permitted work, reassembly and verification of appliance safety devices and gas controls.
Choose a topic to open below
Chimney Standards and Selection
How appliance type, flue route, terminal, materials, air supply and regional rules determine an acceptable system.
Choose a topic to open below
Chimney Inspection and Tests
Inspection and testing methods that establish whether combustion products discharge safely.
Choose a topic to open below
Chimney Installation Practice
Assembly, support, sealing, terminal siting and completion checks for open, balanced and fan-assisted systems.
Choose a topic to open below
Safe Restoration and Relighting
A controlled handback sequence after isolation or work, including tightness, purge, appliance status and user information.
Choose a topic to open below
Reassessment-Only Appliance Work
The limited appliance inspection, test, commissioning and maintenance evidence included only in the CCN1 reassessment route.
Choose a topic to open below
Gas Safety Legislation, Registration and Standards
Apply the correct legal regime and current technical hierarchy while keeping competence evidence, registration and work-category authority distinct.
Key rules
Rule 1
Employers, self-employed operatives and dutyholders must ensure gas work is undertaken by competent people and within the legal conditions that apply.
Exam cue: First identify the nation, premises type, fuel, pressure regime, appliance category and work activity.
Rule 2
Gas Safe registration applies to the business and its operatives; the operative's current ID card categories identify the types of work covered.
Exam cue: Check both the registered business and the operative's current work categories before treating a person as authorised for a task.
Rule 3
CCN1 provides core domestic natural-gas competence evidence, while separate appliance or sector assessments define additional scope.
Exam cue: Use the current assessment-centre document set; do not rely on remembered regulation numbers or superseded editions.
Rule 4
Manufacturer's instructions, legislation, standards and industry procedures must be current and applied in the correct hierarchy.
Exam cue: Separate a legal minimum from best practice and from a manufacturer's more specific instruction.
Rule 5
Great Britain and Northern Ireland have different installation-and-use regulations, and building, housing and carbon-monoxide alarm duties vary across the four nations.
Exam cue: Identify the UK nation and premises type before selecting legislation or guidance.
Study it this way
Scope
Competence, certification and registration are different controls
ACS certification demonstrates assessed competence. Gas Safe registration is the legal registration mechanism, and its work categories constrain what the business and operative may undertake. Neither should be inferred from the other without checking current evidence.
Regional law
Use the law for the work location
Use HSL56 with the Great Britain Regulations where applicable and the Northern Ireland 2004 Regulations for Northern Ireland. Then verify the nation-specific building, housing, high-rise and carbon-monoxide alarm requirements.
Assessment
Learn how to navigate current source documents
ACS permits source material for open-book work, but safe competence means selecting and applying the correct provision. Assessment-centre instructions control the documents and tasks available on the day.
Common traps
Treating a CCN1 pass as permission to work on every domestic gas appliance.
Prevention: Do not treat core certification as automatic appliance-category authority or registration.
Applying HSL56 as though Northern Ireland had the same statutory instrument.
Prevention: Verify instrument suitability, condition, zero and test setup before trusting the result.
Assuming an old certificate or expired card proves current competence and registration.
Prevention: Do not substitute a memorised number or generic sequence for the current procedure that matches the installation.
Using an England Approved Document as a universal UK building rule.
Prevention: Do not substitute a memorised number or generic sequence for the current procedure that matches the installation.
Memory anchors
Authority to Work
Business registration, operative registration category and current competence must all cover the task.
Location First
Identify the UK nation before choosing legislation, building guidance or alarm requirements.
Core Is Not Category
CCN1 is the domestic natural-gas core; appliance work needs the matching additional scope.
Current Documents
Use current law, standards, procedures and manufacturer's instructions—not remembered superseded text.
Specific Wins
A task-specific legal or manufacturer requirement must be considered alongside the general core rule.
Record the Basis
Record what was found, what was measured, what source controlled the decision and what action followed.
Next best moves
Quick check-up
Use a short quiz to confirm the rule pattern is actually sticking.
Check-up Questions
A business sends an operative to replace a domestic boiler. The operative holds current CCN1 but the back of the Gas Safe ID card does not list boilers. What is the correct decision?
Which record is most useful after a compliance decision involving a regional rule?
Answer all questions to submit.
Next step personalized recommendations
Open another topic next
Official resources
Verify the details with the official sources
Use these links for eligibility, scheduling, handbook rules, and issuer updates. Our guide helps you study; official sources tell you what the testing partner currently requires.
CCN1 Issue 19 assessment criteria
IGEM Standard Setting Body page for the March 2026 CCN1 core domestic natural-gas criteria used to preserve the 16-category structure.
IGEM Standard Setting Body
Explains how the SSB maintains competence criteria against legislation and how ACS relates to industry training and competent work types.
NICEIC ACS Domestic Gas Safety
Current UKAS-accredited certification-body overview of CCN1, entry evidence, five-year certification and separate appliance assessments.
ACS scheme rules
Certification-body scheme rules describing written and practical assessment, assessor questioning and approved open-book reference material.
HSE L56 Gas Safety Regulations guidance
HSE Approved Code of Practice and guidance for the Gas Safety (Installation and Use) Regulations 1998 in Great Britain.
HSE Gas Safe registration overview
Explains the legal registration scheme and the importance of checking the work categories on the back of the operative's ID card.
HSENI gas safety and registration
Northern Ireland regulator guidance on Gas Safe registration and the Northern Ireland installation-and-use regulations.
Northern Ireland Gas Safety Regulations 2004
Official legislation text for gas installation and use in Northern Ireland; do not substitute the Great Britain statutory instrument.
BPEC ACS scheme rules and entry guidance
Scheme information including current Guidance Note 8 entry routes, core groups and extension-of-scope controls.
FAQ
Common ACS CCN1 Gas Core questions
Is this an official ACS assessment guide?
No. It is an independent study resource aligned to the public CCN1 criteria and current official or scheme-owner sources. Your chosen certification body and approved assessment centre control entry evidence, documents, assessment tasks and results.
What does the current CCN1 assessment cover?
Issue 19 lists 16 categories: legislation and standards; emergencies; combustion; ventilation; pipework; tightness testing and purging; meter-outlet operating pressure; unsafe situations; isolation controls; burner pressure and gas rate; appliance safety devices; chimney standards; chimney inspection and testing; chimney installation; supply restoration and relighting; and a reassessment-only appliance-work category.
How many questions are on CCN1 and what is the pass mark?
The public Issue 19 criteria do not set out one national paper length, time limit, pass score or topic weighting. ACS assessment includes knowledge and practical evidence, and certification bodies or centres may structure and number their documents differently. Use the current instructions from the centre where you will assess.
Is CCN1 open book?
ACS scheme rules allow approved reference documentation to be provided for open-book questions. That does not make the assessment a simple lookup exercise: the candidate must select the right current source and apply it safely, and the centre controls what documents and materials are permitted.
Does CCN1 let me install, service or repair every domestic gas appliance?
No. CCN1 is the domestic natural-gas core and a prerequisite for many appliance assessments. Real appliance work must also be covered by the relevant assessment and by the operative's current Gas Safe work categories.
Does passing CCN1 automatically make me Gas Safe registered?
No. ACS certification is competence evidence used in the registration process. Regulated gas work must be carried out through a Gas Safe registered business by an appropriately registered operative.
Are the gas rules identical across England, Wales, Scotland and Northern Ireland?
No. CCN1 is a UK competence standard, but the applicable statutory instrument and building, housing, high-rise and carbon-monoxide alarm requirements vary. HSL56 addresses the Great Britain Regulations; Northern Ireland has its own 2004 Regulations. Always verify the nation and premises before selecting the rule.
Can written revision replace workshop preparation?
No. CCN1 requires practical competence in measurement, jointing, testing, purging, combustion analysis, controls, chimney work and restoration. Use current assessment-centre equipment and documents under competent supervision.