CENWAT Flue Requirements & Pressure Relief 6 — Questions and Answers
Question 1: What is 'CE marking' significance for gas boilers sold in the UK post-Brexit?
- CE marking (or UKCA marking for GB market) demonstrates conformity with relevant product safety regulations including the Gas Appliances Regulation (Correct answer)
- CE marking means the boiler has been serviced
- CE marking confirms Gas Safe registration
- CE marking only applies to electrical products
Correct answer: CE marking (or UKCA marking for GB market) demonstrates conformity with relevant product safety regulations including the Gas Appliances Regulation
CE (and now UKCA for the GB market) marking confirms the boiler meets relevant product safety requirements. For gas appliances, this includes compliance with the Gas Appliances Regulation, confirming safe design and construction.
Question 2: What does the Gas Appliances Regulation (formerly Gas Appliances Directive) require?
- All gas appliances placed on the market must be safe, fit for purpose and correctly labelled, with conformity assessed before sale (Correct answer)
- Only that appliances carry a CE mark
- Only that manufacturers register appliances with the HSE
- That all appliances are serviced annually
Correct answer: All gas appliances placed on the market must be safe, fit for purpose and correctly labelled, with conformity assessed before sale
The Gas Appliances Regulation requires gas appliances to be safe, fit for purpose and accompanied by instructions; manufacturers must carry out conformity assessment and apply the CE/UKCA marking before placing appliances on the market.
Question 3: In a room-sealed boiler, what prevents wind from causing dangerous over-pressure in the combustion chamber?
- The pressure-balanced design of the concentric terminal, where wind affects air inlet and flue outlet equally (Correct answer)
- An internal pressure relief valve in the combustion chamber
- A wind deflector fitted to the terminal
- The boiler's gas valve pressure regulator
Correct answer: The pressure-balanced design of the concentric terminal, where wind affects air inlet and flue outlet equally
The concentric terminal design exposes both the air inlet and flue outlet to the same wind conditions, so pressure is balanced and wind does not create a net positive or negative pressure on the combustion system.
Question 4: What is the consequence of insufficient combustion air supply to an open-flued gas appliance?
- Incomplete combustion leading to carbon monoxide production, sooting and potentially dangerous CO levels in the room (Correct answer)
- The boiler simply runs less efficiently with no safety risk
- The boiler automatically switches to a reduced output
- The boiler produces more heat per unit of gas
Correct answer: Incomplete combustion leading to carbon monoxide production, sooting and potentially dangerous CO levels in the room
Insufficient combustion air causes incomplete combustion, producing toxic carbon monoxide (CO) gas, sooting of the heat exchanger and combustion chamber, and potentially dangerous CO levels in the occupied space.
Question 5: What is the function of the overheat thermostat (high limit stat) in a boiler?
- To shut down the boiler if the primary flow temperature exceeds a safe limit, preventing damage and scalding (Correct answer)
- To control normal boiler operating temperature
- To protect the expansion vessel from overheating
- To operate the zone valves if temperature is exceeded
Correct answer: To shut down the boiler if the primary flow temperature exceeds a safe limit, preventing damage and scalding
The overheat (high limit) thermostat is a safety device that cuts off the gas valve if the boiler water temperature exceeds a safe limit, typically 90–95°C, protecting the boiler and system from damage.
Question 6: What is the significance of a yellow flame with black sooty deposits on a gas boiler burner?
- It indicates incomplete combustion, possible carbon monoxide production and a potentially dangerous appliance requiring immediate attention (Correct answer)
- It is normal during initial lighting
- It indicates the appliance is running at peak efficiency
- It indicates the burner needs descaling
Correct answer: It indicates incomplete combustion, possible carbon monoxide production and a potentially dangerous appliance requiring immediate attention
A yellow, sooty flame indicates incomplete combustion due to insufficient air, incorrect gas/air ratio or a blocked burner; it is associated with CO production and the appliance must be made safe immediately.
CENWAT Flue Requirements & Pressure Relief 6
What is 'CE marking' significance for gas boilers sold in the UK post-Brexit?