Gas Safe ACS - Accredited Certification Scheme Appliance Safety Devices Questions and Answers

Question 1

An engineer is servicing a flueless gas cabinet heater. What is the primary function of the Oxygen Depletion Sensor (ODS) fitted to this appliance?

Accepted Answer

To shut off the gas supply if the oxygen level in the room falls below a pre-set safe limit.

Answer

To shut off the gas supply if the carbon monoxide level in the room becomes too high.

Answer

To shut off the gas supply if the flame is extinguished by a draught.

Answer

To automatically increase the ventilation into the room when poor combustion is detected.

Question 2

What is the principal role of a Flame Supervision Device (FSD) on a gas hob burner?

Accepted Answer

To automatically stop the flow of gas to the burner if the flame goes out.

Answer

To regulate the gas pressure to the burner for an efficient flame.

Answer

To detect high levels of carbon dioxide and shut down the appliance.

Answer

To provide the initial spark to ignite the gas at the burner.

Question 3

An engineer is testing an open-flued gas fire and suspects spillage of combustion products. Which safety device is designed to shut down the appliance if it detects a prolonged or serious blockage in the flue?

Accepted Answer

A flue spillage/blocked flue sensor.

Answer

An atmospheric pressure switch.

Answer

A flame rectification probe.

Answer

An over-pressure shut-off (OPSO).

Question 4

While investigating a boiler lockout, an engineer observes water dripping from the discharge pipe of the Pressure Relief Valve (PRV). What is the most likely underlying cause for this?

Accepted Answer

The pressure within the sealed heating system has exceeded its safe operating limit.

Answer

The mains water pressure to the property is too low.

Answer

The gas working pressure at the appliance is incorrect.

Answer

There is a blockage in the boiler's condensate trap.

Question 5

A thermocouple is a common component in a standing pilot assembly. How does it function to ensure safety?

Accepted Answer

It uses two dissimilar metals which, when heated by the pilot flame, generate a small voltage to hold the gas valve open.

Answer

It measures the gas flow rate and closes the valve if it's too high.

Answer

It senses light from the pilot flame and sends a signal to the main control board.

Answer

It expands when heated, physically pushing a valve open to allow gas to flow to the main burner.

Question 6

An engineer is checking the combustion performance of a boiler using a Flue Gas Analyser (FGA) and finds a CO/CO₂ ratio of 0.009. According to BS 7967, how should this reading be interpreted?

Accepted Answer

The appliance is 'At Risk' (AR) and requires servicing and further investigation before being used again.

Answer

The boiler is operating efficiently and safely.

Answer

The appliance requires immediate disconnection as it is 'Immediately Dangerous' (ID).

Answer

The reading is 'Not to Current Standards' (NCS) but the appliance can be left operational.