The ACS CCN1 Core Domestic Gas Safety Certification is a professional certification assessment in United Kingdom. Thorough preparation is essential to demonstrate your knowledge and competency in this field.
Our comprehensive collection of free CCN1 practice questions covers all exam domains and topics. Use these detailed study materials to build confidence and improve your test performance.
Interactive ACS CCN1 resources on PracticeTestGeeks, free to start:
Numbers in brackets link to the official sources listed under Sources & last verified. Dates that have passed are removed automatically.
| Item | Detail | Source · Verified |
|---|---|---|
| Number of questions | Mandatory core assessment; includes Combustion Performance Analysis (CPA1)[1] | niceic.com · Oct 21, 2026 |
| Retake policy | Reassessment every 5 years, often shorter than the initial assessment[1] | niceic.com · Oct 21, 2026 |
| Validity | 5 years[2] | Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr · Oct 24, 2026 |
| Renewal | Renew up to 6 months early without losing time (MOT-style)[1] | niceic.com · Oct 21, 2026 |
| Delivery | In person at an ACS assessment centre (UK)[2] | Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr · Oct 24, 2026 |
| Eligibility | Experienced engineer: held an ACS core or relevant qualification for at least 12 months[3] | Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr · Oct 24, 2026 |
Important: The CCN1 examination requires thorough understanding of all core subject areas. Review the official UK exam guidelines and ensure you meet all eligibility requirements before scheduling your test date.
According to Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr, “Example: Domestic Natural Gas: Core Domestic Gas Safety - CCN1 (mandatory), also includes Combustion Performance Analysis – CPA1”[1]
The content areas below are copied from the official CCN1 content outline published by Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr. The right-hand column shows which of our practice sets covers it.
| Official content area | Practice on this site |
|---|---|
| Checking and setting appliance burner pressures and gas rates[4] | Mixed practice tests above Practise when a pressure or gas rate reading is acceptable, what to do when it is not, and the order of checks at commissioning. |
| Checking operating pressure at outlet of meter[4] | CCN1 Meter and Controls Practise where and how the working pressure is read at the meter outlet and what a low or unstable reading suggests. |
| Chimney Standards[4] | CCN1 Flue Systems and Chimneys Practise the condition, termination and suitability checks for chimneys and flues serving gas appliances. |
| Gas emergency actions and procedures[4] | CCN1 Gas Emergency Procedures Practise the sequence of actions at a suspected gas escape, including isolating supply and keeping people safe. |
| Gas safety legislation and Standards[4] | CCN1 Gas Safety Regulations Practise who is responsible for what under the gas safety regulations, and which standard applies to which task. |
| Installation of pipework and fittings[4] | CCN1 Pipework and Fittings Practise permitted materials, jointing methods, support and routing of pipework in domestic premises. |
| Operation and checking of appliance gas safety devices and controls[4] | CCN1 Meter and Controls Practise how flame supervision and other safety devices work and what a failed device tells you. |
| Operation and positioning of emergency isolation controls and valves[4] | CCN1 Meter and Controls Practise where emergency controls and valves belong and how to confirm they isolate the supply. |
| Products and characteristics of combustion[4] | CCN1 Combustion Principles & Flue Systems Practise complete and incomplete combustion, the products of each, and what they mean for safety. |
| Tightness testing and purging[4] | CCN1 Purging Procedures Practise the order of a tightness test, how to read the result, and safe purging practice. |
| Unsafe situations, emergency notices and warning labels[4] | CCN1 Unsafe Situations Procedure (RIDDOR) Practise classifying an unsafe installation, what to tell the responsible person and which labels and notices apply. |
| Ventilation[4] | CCN1 Combustion and Ventilation Practise working out when extra ventilation is needed and how permanent openings are sized for the appliance. |
Prepare for the ACS CCN1 - Core Domestic Gas Safety exam with our free practice test modules. Each quiz covers key topics to help you pass on your first try.
These are practice questions written for this site, not questions from the real exam. Each explanation shows why the right answer is right and why the others are wrong.
Question: What is the minimum free area of ventilation required for an open-flued gas appliance with a rated input over 7 kW in a room?
Answer: A. 5 cm² per kW of rated input above 7 kW
Explanation:
Option A is right. An open-flued appliance with a rated input over 7 kW needs extra permanent ventilation of 5 cm² of free area for each kW above 7 kW. The first 7 kW is treated as served by normal air leakage in the room.
Option B is wrong because it applies the figure to the whole rated input, including the part that needs no extra opening. Option C uses a larger figure than the one required, so it over-sizes the opening. Option D is wrong because above the 7 kW threshold an additional opening is required, not optional.
Rule to remember: subtract the threshold from the rated input first, then apply the per-kW free area to the difference only, never to the total.
Question: Under the Gas Safety (Installation and Use) Regulations 1998, who is legally responsible for ensuring gas appliances are maintained in a safe condition in rented properties?
Answer: B. The landlord or property owner
Explanation:
Option B is right. Under the Gas Safety (Installation and Use) Regulations, a landlord must make sure the gas appliances, fittings and flues they provide for tenants are maintained in a safe condition, and must have them checked by a Gas Safe registered engineer.
Option A is wrong because a tenant does not take on the landlord's legal duty for equipment the landlord supplies. Option C is wrong because local authority building control approves building work and does not carry out the maintenance duty. Option D is wrong because a manufacturer is responsible for the product it makes, not for upkeep in a rented home.
Rule to remember: the duty follows who provides the appliance and lets the property, so for rented homes ask who the landlord is.
Question: What material must NOT be used for gas pipework installations in the UK?
Answer: A. Lead — lead pipework is prohibited for gas installations due to its toxicity and poor joint integrity
Explanation:
Option A is right. Lead must not be used for gas pipework. It is prohibited because it is toxic and its joints are not reliable for carrying gas.
Option B is wrong because copper is an approved material for gas pipework when joined by an approved method. Option C is wrong because steel with threaded joints is acceptable, so the claim that only press-fit is permitted is false. Option D is wrong because not all plastic is prohibited; some approved plastic systems are used, usually underground.
Rule to remember: be suspicious of any option that says a whole material family is banned or that only one jointing method is allowed. The real prohibition here is lead, and approved materials still need approved joints.
Start by reading the official ACS and IGEM assessment information so you know what your centre will test and how it is run. Then take the free CCN1 practice test to find your weak areas before you spend time on any single topic.
Work through the topic sets in the order that suits your gaps. If combustion and ventilation questions feel slow, do those sets next, then flue systems and chimneys. Treat pipework, tightness testing and purging as a group, because the procedures lead on from each other. Give gas emergencies, unsafe situations and the regulations their own sessions, since those answers depend on exact procedure and responsibility rather than on calculation.
After each set, read every explanation, including those for questions you got right. For each miss, write the rule in a sentence in your own words and check it against the standard or regulation it comes from. Our questions are practice material written by us, so the official documents stay the authority when the two differ.
Leave a few days before your assessment for repeat attempts on the sets where you scored lowest, and finish with a timed run of the free practice test. If you are renewing, remember you can book up to 6 months before expiry without losing time, so you need not wait until the last moment to start revising.
Join thousands of candidates who have used our free practice tests to prepare for the ACS CCN1 Core Domestic Gas Safety Certification. Start practising today and build the confidence you need to succeed. Practice with the free ACS CCN1 practice test on PracticeTestGeeks (7 questions with answer explanations).
Try these questions from our free ACS CCN1 practice tests. The correct answer and an explanation follow each question.
What percentage of CO2 would you typically expect in the flue gases of a correctly adjusted natural gas boiler?
Answer: C. 7–9%
A correctly adjusted natural gas boiler running with the appropriate amount of excess air should produce approximately 7–9% CO2 in the flue gases, indicating efficient combustion.
What is the stoichiometric air-to-gas ratio for natural gas combustion?
Answer: A. Approximately 10 parts air to 1 part gas by volume
The stoichiometric (theoretically perfect) combustion of natural gas requires approximately 10 volumes of air per volume of gas. In practice, a small excess of air is provided to ensure complete combustion.
What is the purpose of a draught diverter (draught break) fitted to an open-flued gas appliance?
Answer: B. To prevent excessive draught (down-draught or up-draught) affecting the burner and to allow dilution air to enter the flue
A draught diverter stabilises the draught conditions at the appliance by preventing excessive variations in flue pull from affecting the burner. It allows dilution air from the room to enter the flue, which helps to maintain steady combustion conditions. It also provides a point at which spillage of combustion products can be detected during a spillage test.
What is the purpose of purging a gas installation after completing pipework installation or modification?
Answer: B. To remove air from the pipework and replace it with gas, preventing a potentially explosive air-gas mixture
Purging removes the air from newly installed or modified gas pipework and replaces it with gas. This is essential because a mixture of air and gas within the pipe could form an explosive mixture. Purging must be carried out safely in accordance with IGE/UP/1B, ensuring proper ventilation and that no ignition sources are present.
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