CCN1 Meter and Controls

Question 1

What is the purpose of the Emergency Control Valve (ECV) on a domestic gas meter?

Accepted Answer

To allow the gas supply to be turned off in an emergency

Answer

The Emergency Control Valve (ECV) is a quarter-turn valve fitted to the gas meter that allows the entire gas supply to the property to be shut off quickly in an emergency. When the handle is perpendicular to the pipe, the valve is closed. Only Gas Safe registered engineers or National Gas Emergency Service operatives should operate the ECV on the upstream side of the meter.

Question 2

A gas engineer needs to check the standing pressure at a domestic meter. What reading should they expect under normal conditions?

Accepted Answer

21 mbar

Answer

The normal standing pressure (static pressure) at a domestic gas meter in the UK should be approximately 21 mbar. This is measured with all appliances turned off (no gas flowing). The working pressure (with appliances operating) should not drop below 19 mbar at the meter. A significant deviation may indicate a supply problem.

Question 3

What type of thermostat is designed to shut off the gas supply to a boiler if the water temperature exceeds a safe limit?

Accepted Answer

Overheat thermostat (limit thermostat)

Answer

An overheat thermostat (also called a limit thermostat or high-limit thermostat) is a safety device that shuts off the gas supply to the boiler if the water temperature exceeds a predetermined safe limit (typically around 85-90°C). This prevents the system from reaching dangerously high temperatures and pressures. It is a non-self-resetting device that requires manual reset.

Question 4

What is the function of a flame supervision device (FSD) on a gas appliance?

Accepted Answer

To shut off the gas supply to the burner if the flame is extinguished, preventing a gas escape

Answer

A flame supervision device (FSD), such as a thermocouple, flame rectification probe, or mercury vapour capsule, monitors the presence of a flame at the burner. If the flame is extinguished for any reason, the FSD closes the gas valve to prevent unburnt gas from escaping into the room. This is a critical safety device on all modern gas appliances.

Question 5

What does a pressure regulator (governor) on a gas meter do?

Accepted Answer

Reduces and maintains the outlet pressure at a constant 21 mbar

Answer

The pressure regulator (governor), typically integrated into the gas meter, reduces the incoming mains pressure to a stable outlet pressure of 21 mbar for domestic supplies. This ensures that appliances receive a consistent supply pressure regardless of fluctuations in the mains pressure.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Meter and Controls