CCN1 Gas Appliance Installation and Commissioning 2

Question 1

What is the acceptable CO/CO2 ratio in flue gas for a correctly adjusted natural gas boiler?

Accepted Answer

Below 0.004

Answer

A CO/CO2 ratio below 0.004 indicates efficient and complete combustion in a correctly adjusted natural gas boiler; a ratio above 0.004 indicates incomplete combustion requiring investigation.

Question 2

What is the correct working gas pressure for natural gas at a domestic appliance inlet, measured while the appliance is operating at full load?

Accepted Answer

20 mbar

Answer

The working pressure for natural gas at a domestic appliance inlet should be 20 mbar when measured with the appliance operating at full load, slightly below the 21 mbar standing pressure.

Question 3

When commissioning an open-flued gas appliance, which test confirms that the flue is performing correctly and removing combustion products safely?

Accepted Answer

A spillage test using a smoke match or smoke pellet

Answer

A spillage test using a smoke match or smoke pellet placed near the draught diverter confirms that combustion products are being safely drawn up and out of the flue rather than spilling into the room.

Question 4

What should an engineer do if a gas appliance cannot achieve the correct working pressure during commissioning?

Accepted Answer

Do not commission the appliance and investigate the cause of the low pressure

Answer

An appliance that cannot achieve its design working pressure must not be commissioned, as incorrect gas pressure leads to incomplete combustion, poor efficiency, and potentially dangerous operating conditions.

Question 5

What is the primary reference document for setting the correct burner pressure on a gas appliance during commissioning?

Accepted Answer

The appliance manufacturer's installation instructions

Answer

The appliance manufacturer's installation instructions specify the exact burner pressure settings for that appliance, and these must always be followed during commissioning as they are specific to each appliance design.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Gas Appliance Installation and Commissioning 2