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GasRevise · Pass your ACS

Gas ACS exam revision

Prepare for UK domestic gas assessments with safety scenarios, diagrams and worked calculations. Start with 25 free CCN1 questions, or use the same set for a mock test. No account needed. Premium unlocks the full gas bank and longer mock assessments.

  • 1,386 exam-style questions
  • 119 study notes
  • 9 modules

Core Safety & Unsafe Situations

The foundation: classify unsafe situations, test for tightness, and get ventilation, flueing and emergencies right.

25 free questions
CCN1

Core Domestic Gas Safety

The core module everything else builds on — classifying unsafe situations, tightness testing, ventilation, flueing and emergency actions.

Unsafe situations (ID / AR / NCS)Tightness testing & purgingVentilation & flueingEmergency procedures

378 questions 37 study notes

LearnQuestions

Boilers, Controls & Commissioning

Boilers and water heaters — controls, interlock and the commissioning sequence.

Reading the Flue Gases

What the analyser is telling you, and when an appliance is not safe to leave running.

Unvented Hot Water & Water Regs

Two tickets often taken alongside gas and well worth holding in their own right — unvented hot water (G3) and the Water Regulations (WRAS).

Appliance Specialisms

The appliance-specific checks — cookers, fires, meters and LPG changeover.

Premium
CONGLP1

LPG Changeover

Changing a property over from natural gas to LPG — the safety differences that matter most (LPG is heavier than air).

LPG vs natural gasPressures & tightnessStorage & siting

99 questions 4 study notes

LearnQuestions

Choose how to practise for your gas exam

For feedback after each answer, start with CCN1 practice questions. For a mixed set with an optional timer, set up a CCN1 mock test. Choose 5, 10 or all 25 free questions, switch the practice timer on or off, get feedback as you answer, then review your result after submitting.

Both modes use the same free questions, so a repeat score includes familiarity. Our test lengths and timers are revision settings; your assessment centre confirms its assessment arrangements. Use the CCN1 questions and answers guide to plan your review, then return to the free CCN1 notes for the topics you missed.

How the domestic gas ACS fits together

ACS is a competence assessment, not a course or a “level” — it is how you prove you can work on gas safely and legally and get onto the Gas Safe Register. Everything builds on CCN1, the core domestic gas safety module covering tightness testing, ventilation, flueing, unsafe situations and the core calculations. On top of CCN1 you add the appliance modules for the work you actually do: CENWAT for boilers and water heaters, CKR1 for cookers, HTR1 for fires and wall heaters, MET1 for meters, and CPA1 for combustion analysis.

What to revise first

Get CCN1 solid before anything else — if the core is rusty, every appliance module gets harder than it needs to be. Prioritise unsafe situations (ID and AR, with safe standards shortfalls recorded separately), the calculations (gas rate, heat input, ventilation free area and the CO/CO₂ ratio) and the emergency actions. The CCN1 revision plan breaks this into a week you can follow, and the ACS assessment explained covers what the day looks like, resits and pass marks.

New entrant or reassessing?

New entrants usually come through a managed learning programme with supervised on-site experience before sitting the assessments — see how to become Gas Safe registered. Existing engineers reassess roughly every five years, and the parts that catch experienced hands are the written classifications and calculations they use less often, which is exactly what the reassessment checklist is built for.

Free vs Premium

The CCN1 core notes and 25 selected questions are free, with no account needed. Start CCN1 practice to work through safety decisions, diagrams and calculations. Premium unlocks the full gas question bank across every module and longer timed mock assessments to help you find and revisit your weak spots.