CCN1 Practice Test

Free ACS CCN1 Study Tools

Interactive ACS CCN1 resources on PracticeTestGeeks, free to start:

• CCN1 Gas Appliance Installation and Commissioning 1 — 7 questions with answer explanations
• ACS CCN1 flashcards — review key terms and concepts card by card
• ACS CCN1 study guide — topic-by-topic overview of what the exam covers
• ACS CCN1 cheat sheet — one-page printable summary for last-minute review

CCN1 Exam at a Glance

CCN1 Study Tips

• Create a structured study schedule at least 4-6 weeks before your CCN1 exam date.
• Focus on understanding core concepts rather than memorising answers for the ACS CCN1 Core Domestic Gas Safety Certification.
• Use our free practice tests to identify weak areas and track your progress over time.
• Review the official CCN1 exam syllabus to ensure complete topic coverage.
• Take timed practice sessions to build your exam pace and reduce test-day anxiety.

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]

CCN1 content outline and where to practise each area

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.

Worked examples: how to reason through CCN1 questions

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.

Example 1

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?

1. 5 cm² per kW of rated input above 7 kW
2. 5 cm² for every kW of rated input
3. 10 cm² per kW of rated input above 7 kW
4. No additional ventilation is required

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.

Example 2

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?

1. The tenant occupying the property
2. The landlord or property owner
3. The local authority building control
4. The gas appliance manufacturer

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.

Example 3

Question: What material must NOT be used for gas pipework installations in the UK?

1. Lead — lead pipework is prohibited for gas installations due to its toxicity and poor joint integrity
2. Copper — it is not suitable for gas
3. Steel with threaded joints — only press-fit is permitted
4. Plastic — all plastic pipework is prohibited for gas

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.

How to use these practice tests

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.

Ready to Pass the CCN1?

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).

Sample ACS CCN1 Practice Questions

Try these questions from our free ACS CCN1 practice tests. The correct answer and an explanation follow each question.

1. What percentage of CO2 would you typically expect in the flue gases of a correctly adjusted natural gas boiler?

   • A. Less than 3%
   • B. 4–6%
   • C. 7–9%
   • D. 12–14%

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.

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.

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.

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.

Take the full ACS CCN1 practice test

Sources & last verified

1. niceic.com — number of questions, retake policy, renewal (official source). “Example: Domestic Natural Gas: Core Domestic Gas Safety - CCN1 (mandatory), also includes Combustion Performance Analysis – CPA1” Verified Oct 21, 2026 · source checked Oct 21, 2026.
2. Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr — validity, delivery (official source). “Gas Safe Registered engineers are required to renew their certificates of competency every 5 years, and this can be done either by ACS renewal or…” Verified Oct 24, 2026 · source checked Oct 24, 2026.
3. Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr — eligibility (official source). “Experienced Engineer: An engineer who is registered or previously registered on GSR. The engineer must be in possession of or previously held an ACS core…” Verified Oct 24, 2026 · source checked Oct 24, 2026.
4. Nationally Accredited Certification Scheme for Individual Gas Fitting Operatives (ACS). The assessment criteria and entr — other (official source). “checking and setting appliance burner pressures and gas rates” Verified Nov 1, 2026.

How we verify: editorial & fact-checking policy. Report an error: contact us.