Gas Safe CCN1 Core Prep: Free Mock Test & Practice Questions

Gas Safe CCN1 Core Prep

Core domestic gas safety (ACS CCN1) revision questions.

Pass mark 30/40 60 minutes Gas Safe/ACS How many can I get wrong?

Sit a full mock under the clock at least once. Nerves are half the battle.

Free practice questions

Try 3 real Gas Safe CCN1 Core Prep questions

Have a go, then reveal the worked explanation. A taster from a bank of 219 original questions — unlock for unlimited drills and full timed mocks.

Q1. Under the Gas Safety (Installation and Use) Regulations 1998 (GSIUR), who is legally responsible for ensuring that any gas appliance, fitting, flue or pipework they install is safe?

A. The installer who carries out the work
B. The householder who commissioned the work
C. The gas supplier delivering to the property
D. The local authority building control officer

Show answer & explanation

✓ Answer: A. The installer who carries out the work

GSIUR places the duty on the person carrying out the installation work to ensure it is done safely and left in a safe condition. The householder has separate landlord-type duties only if they are also a landlord; the gas supplier and building control have no role in installation safety under GSIUR.

Q2. Why is carbon monoxide particularly dangerous compared with many other combustion products?

A. It is heavier than air and only collects at floor level
B. It has a strong smell that is easily detected before harm occurs
C. It is highly flammable at very low concentrations in air
D. It is colourless, odourless and binds to haemoglobin more readily than oxygen

Show answer & explanation

✓ Answer: D. It is colourless, odourless and binds to haemoglobin more readily than oxygen

Carbon monoxide has no colour, taste or smell, so victims are often unaware of exposure. It binds to haemoglobin around 200-300 times more readily than oxygen, forming carboxyhaemoglobin and starving the body of oxygen, which is why undetected exposure is so dangerous.

Q3. During a let-by test, the installation is isolated at the emergency control valve. What result indicates the ECV itself may be letting by?

A. The pressure continues to rise after isolation
B. The pressure remains completely static after isolation
C. The pressure falls sharply and continues to fall
D. The gauge reading drops to zero instantly

Show answer & explanation

✓ Answer: A. The pressure continues to rise after isolation

If pressure continues to rise after the ECV has been closed and the downstream side isolated, this shows gas is still passing through the closed valve, indicating the ECV itself is letting by rather than the fault lying in the customer's pipework. A static reading after isolation would instead suggest the downstream pipework is sound.

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Gas Safe CCN1 Core Prep — common questions

Frequently asked

How many questions are in the Gas Safe CCN1 Core Prep?

The exam has 40 questions. Every Revision Robin mock uses the same 40-question format so your practice matches the real thing.

What is the pass mark for the Gas Safe CCN1 Core Prep?

You need 30 out of 40 correct to pass, which is about 75%. Our mocks mark you against this exact threshold.

How long do you get?

The test is timed at 60 minutes. Our full mock runs on the same clock so you can practise your pacing.

Are these the real exam questions?

No. Our questions are original and written to match the current syllabus, so they give realistic practice without copying the official paper. Every answer comes with a plain-English explanation. Always confirm current rules and content with Gas Safe/ACS.