ACS Study Guide 2026
Everything you need to pass the ACS exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 ACS Exam Format at a Glance
📚 ACS Topics to Study (33)
✍️ Sample ACS Questions & Answers
1. What does 'approved' mean when referring to gas appliances and fittings under GSIUR 1998?
Gas appliances must carry CE or UKCA marking (post-Brexit) demonstrating conformity with the Gas Appliances Regulation — using unapproved appliances is a breach of GSIUR 1998.
2. What does the term 'dead leg' mean in gas pipework?
A dead leg is a capped pipe run left in the installation from a previous appliance — it retains gas in the unused section and represents an unnecessary length of pressurised pipe that should ideally be removed.
3. What is the minimum separation distance between a gas meter box and an electricity meter box when installed externally on a building?
Gas and electricity meters must be separated by sufficient distance to prevent gas accumulation near electrical equipment that could cause ignition — network operator standards specify the precise separation required.
4. What is the correct procedure for locating a gas leak using a leak detection fluid?
Leak detection fluid (or electronic detector) is applied to pressurised joints while gas is flowing; bubbles indicate a leak at that point — a systematic approach from meter to appliance is used.
5. What is the purpose of a 'draught diverter' on an open-flued appliance?
A draught diverter introduces dilution air between the heat exchanger and flue, neutralising the effect of negative or positive pressure fluctuations in the flue and preventing them from disrupting combustion.
6. An engineer is installing 22mm copper pipework to supply a domestic gas boiler. According to BS 6891, what is the correct method for protecting this pipework where it passes through a solid wall?
BS 6891 and Regulation 19 of GSIUR 1998 require that when gas pipework passes through a solid wall or floor, it must be protected. The correct method is to place the pipe inside a suitable sleeve that runs the full width of the structure. The space between the gas pipe and the sleeve (the annular space) must be sealed at one end to prevent gas from an escape tracking into the building's structure, while allowing for ventilation or minor movement at the other.