Gas Safe ACS - Accredited Certification Scheme Chimney and Flue Systems Questions and Answers — Questions and Answers
Question 1: An engineer is installing a new, room-sealed, fanned-draught boiler. According to BS 5440-1, what is the minimum horizontal distance required between the centre of the flue terminal and an opening window on the same wall?
- 600 mm
- 150 mm
- 300 mm (Correct answer)
- 1200 mm
Correct answer: 300 mm
BS 5440-1 specifies the minimum clearances for flue terminals to prevent products of combustion from re-entering the property. For a fanned-draught, room-sealed appliance, the minimum horizontal distance from the centre of the terminal to an opening (such as a window or door) is 300 mm.
Question 2: When performing a spillage test on a conventional open-flued appliance, after allowing it to operate for an initial period, what is the minimum duration the smoke test should be observed at the draught diverter opening?
- 30 seconds
- 5 minutes
- Until the smoke pellet is fully extinguished
- 2 minutes (Correct answer)
Correct answer: 2 minutes
The standard procedure for a spillage test requires the engineer to observe the smoke from a smoke match or pellet at the edge of the draught diverter. After an initial warm-up period, if spillage occurs, the appliance is left to run for a further 10 minutes and then re-tested. The smoke test itself must be observed for a period of 2 minutes to ensure all products of combustion are being safely removed by the flue.
Question 3: An engineer is assessing a masonry chimney for use with a new inset live fuel effect gas fire. Which of the following is a primary requirement before the appliance can be installed?
- The chimney must be fitted with a specific anti-downdraught cowl.
- The chimney must be swept, and its integrity and suitability confirmed, being lined if necessary. (Correct answer)
- The top of the chimney stack must be at least 1 metre higher than any neighbouring property's roof.
- The chimney must have a minimum internal diameter of 200 mm throughout its entire length.
Correct answer: The chimney must be swept, and its integrity and suitability confirmed, being lined if necessary.
Before using an existing masonry chimney for a gas appliance, its safety and suitability must be established. This involves having the chimney thoroughly swept to remove soot and blockages, followed by an integrity test (e.g., a smoke test) to ensure there are no leaks. If the chimney fails the test or is otherwise unsuitable (e.g., too large), it must be relined with a suitable flue liner specified for gas appliances.
Question 4: While servicing a condensing boiler, an engineer finds that the plastic flue pipe runs through an unheated loft space but has not been insulated. What is the primary safety concern associated with this installation fault?
- The flue pipe may become brittle and crack due to UV light exposure.
- The uninsulated pipe will cause excessive heat loss from the property.
- Condensate within the flue could freeze, leading to a blockage and appliance shutdown or malfunction. (Correct answer)
- The noise of the condensate running down the pipe will be unacceptably loud.
Correct answer: Condensate within the flue could freeze, leading to a blockage and appliance shutdown or malfunction.
Condensing boilers produce acidic condensate as a by-product of combustion. This liquid flows back down the flue system to a drain. In unheated areas like a loft or garage, this condensate can freeze during cold weather, creating an ice blockage in the flue. This blockage will activate the boiler's safety sensors and cause it to shut down, or in a worse-case scenario, lead to the unsafe operation of the appliance. Manufacturer's instructions and industry standards require the flue to be insulated in such spaces to prevent this.
Question 5: An engineer is called to a property where the homeowner reports fumes from an open-flued gas fire. The engineer finds the flue is completely blocked by a bird's nest. How should this situation be classified according to the Gas Industry Unsafe Situations Procedure (GIUSP)?
- Immediately Dangerous (ID) (Correct answer)
- At Risk (AR)
- Not to Current Standards (NCS)
- Requires Specialist Investigation (RSI)
Correct answer: Immediately Dangerous (ID)
An 'Immediately Dangerous' (ID) situation is one that poses an immediate danger to life or property. A completely blocked flue on an open-flued appliance will cause the products of combustion, including poisonous carbon monoxide, to spill directly into the room. This presents a severe and immediate risk to the occupants, and therefore must be classified as ID. The engineer must immediately turn off the appliance, isolate the gas supply to it, and issue a warning notice.
Question 6: What is the defining characteristic of a 'room-sealed' gas appliance?
- It must be installed in a room with a permanent, sealed air vent to outside.
- Its combustion circuit (air intake and flue outlet) is sealed from the room it is installed in. (Correct answer)
- All of its external joints and seams are sealed with a high-temperature waterproof sealant.
- It can only be installed in rooms with a volume greater than 10 cubic metres.
Correct answer: Its combustion circuit (air intake and flue outlet) is sealed from the room it is installed in.
A room-sealed appliance is designed so that its entire combustion process is isolated from the living space. It draws its air for combustion from outside the building and expels the products of combustion back outside, typically through a concentric (pipe-within-a-pipe) balanced flue. This design prevents it from using the air within the room and ensures that no flue gases can escape into the property, making it a very safe type of appliance.
Gas Safe ACS - Accredited Certification Scheme Chimney and Flue Systems Questions and Answers
An engineer is installing a new, room-sealed, fanned-draught boiler.
According to BS 5440-1, what is the minimum horizontal distance required between the centre of the flue terminal and an opening window on the same wall?