CENWAT Flue Requirements & Pressure Relief 2 — Questions and Answers
Question 1: What must be done if a gas boiler flue terminal is within 1 metre of a window?
- A plume management kit must be fitted or the terminal repositioned to achieve the minimum clearance (Correct answer)
- Nothing — 1 m is sufficient clearance
- A CO alarm must be fitted within 1 m
- The window must be permanently sealed
Correct answer: A plume management kit must be fitted or the terminal repositioned to achieve the minimum clearance
If a flue terminal is closer than the minimum required clearance to an openable window, a plume management kit can redirect the flue exhaust to an acceptable position, or the terminal must be relocated.
Question 2: What is a plume management kit?
- An extension that redirects the condensate plume and flue gas exhaust upwards or away from windows and openings (Correct answer)
- A device to suppress noise from the flue fan
- A kit to extend the flue for longer runs
- A kit to increase flue draught on older boilers
Correct answer: An extension that redirects the condensate plume and flue gas exhaust upwards or away from windows and openings
A plume management kit redirects the white condensate plume from a condensing boiler's flue terminal away from windows, doors and pathways where it may cause nuisance or re-enter the building.
Question 3: What is the minimum clearance required between a gas boiler flue terminal and a gas meter?
- 300 mm (Correct answer)
- 100 mm
- 1000 mm
- 50 mm
Correct answer: 300 mm
A flue terminal must not be within 300 mm of a gas meter, regulator or any meter housing to prevent gas ignition if there is a minor gas leak at the meter.
Question 4: What action should be taken if a flue is found to be leaking flue gases into a room?
- Immediately turn off the appliance, ventilate the room, warn occupants and do not use until repaired (Correct answer)
- Increase the boiler thermostat to improve draught
- Fit an additional CO detector
- Increase the fan speed
Correct answer: Immediately turn off the appliance, ventilate the room, warn occupants and do not use until repaired
A leaking flue is an immediately dangerous (ID) situation; the appliance must be shut down immediately, the room ventilated, occupants warned, and the appliance made safe before use.
Question 5: What is the maximum CO level in a flue gas (as measured at the flue terminal) that is generally considered acceptable for a gas boiler?
- CO:CO2 ratio below 0.004 (or as specified by the manufacturer's commissioning data) (Correct answer)
- CO below 100 ppm
- CO below 500 ppm
- Any level is acceptable at the terminal
Correct answer: CO:CO2 ratio below 0.004 (or as specified by the manufacturer's commissioning data)
The CO:CO2 ratio method is used to assess combustion quality; a ratio above 0.004 may indicate incomplete combustion and requires investigation. Absolute CO limits vary by manufacturer.
Question 6: What is the purpose of the pressure relief valve (PRV) in a sealed central heating system?
- To open and discharge water if system pressure exceeds the set point, typically 3 bar, protecting the system from over-pressure (Correct answer)
- To maintain minimum system pressure
- To regulate boiler operating pressure
- To act as a non-return valve
Correct answer: To open and discharge water if system pressure exceeds the set point, typically 3 bar, protecting the system from over-pressure
The PRV is a safety device that automatically opens at its set pressure (typically 3 bar) to discharge water, preventing dangerous over-pressure which could damage components or cause failure.
CENWAT Flue Requirements & Pressure Relief 2
What must be done if a gas boiler flue terminal is within 1 metre of a window?