Gas Safe ACS - Accredited Certification Scheme Burner Pressures and Gas Rates Questions and Answers

Question 1

An engineer is commissioning a new boiler with a manufacturer's stated gross heat input of 24 kW.
Using a metric meter, they time the gas consumption and record that it takes 135 seconds to burn 0.1 m³.
The declared calorific value (CV) of the natural gas is 40.0 MJ/m³.
How does the calculated heat input compare to the manufacturer's specification?

Accepted Answer

It is significantly above the acceptable tolerance of +/- 5%.

Answer

It is within the acceptable tolerance of +/- 5%.

Answer

It is significantly below the acceptable tolerance of +/- 5%.

Answer

The calculation cannot be completed without the net heat input value.

Question 2

What is the primary purpose of an engineer measuring the burner operating pressure at an appliance's test point during servicing?

Accepted Answer

To ensure the gas is being delivered to the burner at the correct pressure for safe and efficient combustion.

Answer

To confirm the standing pressure at the meter is adequate for the installation.

Answer

To verify that the gas rate is within the manufacturer's specified tolerance.

Answer

To check that the appliance gas valve is not letting-by when closed.

Question 3

An engineer is checking the gas rate of an appliance and finds it to be significantly lower than the manufacturer's stated heat input. Which of the following is the most likely cause?

Accepted Answer

Inadequate working pressure at the appliance inlet.

Answer

The appliance has been fitted with an injector for LPG instead of Natural Gas.

Answer

The calorific value of the gas is higher than the standard value.

Answer

The gas meter is oversized for the property's total load.

Question 4

While servicing a room-sealed boiler, an engineer measures the burner operating pressure. The manufacturer's data plate states the pressure should be 14.0 mbar ± 1.0 mbar. The engineer records a stable reading of 10.5 mbar and the flame picture is visibly poor. In accordance with the Gas Industry Unsafe Situations Procedure (GIUSP), how should this be classified?

Accepted Answer

At Risk (AR)

Answer

Immediately Dangerous (ID)

Answer

Not to Current Standards (NCS)

Answer

Requires Verbal Advice (RVA)

Question 5

When an engineer performs a gas rate check on a domestic appliance, the calculated heat input must be compared against the manufacturer's stated figure. What is the generally accepted industry tolerance for this check?

Accepted Answer

± 5%

Answer

± 15%

Answer

± 10%

Answer

± 2.5%

Question 6

During a service, an engineer finds the burner pressure of a gas fire is significantly higher than specified in the manufacturer's instructions, although the working pressure at the appliance inlet is correct. What is the most probable cause of this fault?

Accepted Answer

The burner injector is partially blocked with debris.

Answer

The meter regulator is failing and causing a pressure surge.

Answer

The wrong type of injector has been fitted (one with a larger orifice).

Answer

A partial blockage in the flue is causing back pressure.