CCN1 Gas Appliance Installation and Commissioning 1 — Questions and Answers
Question 1: What is the minimum distance a room-sealed balanced flue terminal must be from an openable window or air vent?
- 150mm
- 300mm (Correct answer)
- 600mm
- 1200mm
Correct answer: 300mm
BS 5440 Part 1 requires a room-sealed appliance flue terminal to be at least 300mm from any openable window, air vent, or opening to prevent combustion products from re-entering the building.
Question 2: Which document must be completed and left with the customer after commissioning a new gas boiler?
- Gas Safe registration certificate
- Benchmark commissioning checklist (Correct answer)
- Local authority building notice
- CORGI registration form
Correct answer: Benchmark commissioning checklist
The Benchmark commissioning checklist must be completed and handed to the customer as proof that the appliance has been correctly installed, commissioned, and is operating to the manufacturer's specification.
Question 3: What type of gas appliance does NOT require a permanent air vent in the room where it is installed?
- Open-flued appliance rated above 7kW
- Flueless catalytic space heater
- Room-sealed (balanced flue) appliance (Correct answer)
- Open-flued appliance rated below 7kW
Correct answer: Room-sealed (balanced flue) appliance
Room-sealed appliances draw combustion air directly from outside and discharge products of combustion outside, so they have no effect on the room's air quality and do not require a permanent air vent.
Question 4: What is the correct standing (static) gas pressure for natural gas at a domestic meter outlet?
- 10 mbar
- 17 mbar
- 21 mbar (Correct answer)
- 37 mbar
Correct answer: 21 mbar
The standard standing pressure for natural gas at a domestic meter outlet is 21 mbar, measured with no gas flowing; working pressure when gas is flowing is typically 20 mbar.
Question 5: Which primary legislation requires all gas work on domestic premises to be carried out by a Gas Safe registered engineer?
- The Health and Safety at Work Act 1974
- The Gas Act 1986
- The Gas Safety (Installation and Use) Regulations 1998 (Correct answer)
- The Building Regulations 2010
Correct answer: The Gas Safety (Installation and Use) Regulations 1998
The Gas Safety (Installation and Use) Regulations 1998 (GS(IU)R) specifically require that all gas work on domestic premises must be carried out by a competent Gas Safe registered engineer.
Question 6: Before commissioning a new gas appliance, what electrical checks must the engineer perform?
- Verify the supply voltage is exactly 230V
- Confirm the circuit uses 2.5mm² cable throughout
- Check that the appliance is correctly earthed and that polarity is correct (Correct answer)
- Ensure a 30mA RCD protects the appliance circuit
Correct answer: Check that the appliance is correctly earthed and that polarity is correct
The engineer must verify correct earthing and electrical polarity before commissioning any gas appliance with an electrical supply, as incorrect earthing or reversed polarity can create a serious safety hazard.
Question 7: Why is checking the gas rate important during appliance commissioning?
- To detect gas leaks in the pipework
- To verify the appliance is consuming gas within its designed input (Correct answer)
- To test the accuracy of the gas meter
- To set the correct thermostat calibration
Correct answer: To verify the appliance is consuming gas within its designed input
Checking the gas rate by timing the meter confirms that the appliance is operating within its designed input rating, ensuring efficient combustion and safe operation in line with the manufacturer's specification.
CCN1 Gas Appliance Installation and Commissioning 1
What is the minimum distance a room-sealed balanced flue terminal must be from an openable window or air vent?