CENWAT Pipework Sizing and Installation 2 — Questions and Answers
Question 1: What type of fitting is NOT permitted for making joints on gas pipework concealed within walls?
- Soldered capillary fittings
- Compression fittings (Correct answer)
- Press-fit fittings with gas-approved seals
- Brazed joints
Correct answer: Compression fittings
Compression fittings must NOT be used on gas pipework that is concealed within walls, floors, or where not readily accessible. Only permanent joints such as soldered capillary, brazed, or approved press-fit fittings with gas-specific seals may be used in concealed locations, as compression fittings can loosen over time.
Question 2: What is the minimum fall required on a condensate pipe from a condensing boiler?
- No fall required, it can be installed level
- A minimum fall of 2.5 degrees, approximately 44mm per metre (Correct answer)
- A minimum fall of 1 degree, approximately 17mm per metre
- A minimum fall of 5 degrees, approximately 87mm per metre
Correct answer: A minimum fall of 2.5 degrees, approximately 44mm per metre
The condensate discharge pipe should have a minimum continuous fall of 2.5 degrees, approximately 44mm per metre run, toward the drain point. The key requirement is a continuous fall with no traps where condensate could collect and freeze.
Question 3: What is the purpose of a magnetic system filter installed on the return pipe of a central heating system?
- To filter the mains water supply
- To capture magnetic iron oxide sludge (magnetite) from the system water (Correct answer)
- To regulate the water pressure
- To measure the flow rate
Correct answer: To capture magnetic iron oxide sludge (magnetite) from the system water
A magnetic system filter is installed on the return pipe close to the boiler to capture magnetic iron oxide particles (magnetite) from the circulating system water. Magnetite is a product of internal corrosion and if not removed can block the boiler heat exchanger and damage pump seals.
Question 4: What is the minimum insulation thickness required for central heating pipework in unheated areas under Building Regulations Part L?
- No insulation required
- Equal to the pipe diameter
- 19mm for pipes up to 22mm diameter (Correct answer)
- 25mm for all pipe sizes
Correct answer: 19mm for pipes up to 22mm diameter
Building Regulations Part L requires that central heating pipework in unheated areas such as lofts, garages, and under floors must be insulated. For pipes up to 22mm diameter, the minimum insulation thickness is 19mm with a material having a thermal conductivity of 0.035 W/mK.
Question 5: When sizing radiators for a room, which heat loss calculation method is commonly used in the UK?
- Simply matching radiator output to room volume
- Using the U-value method considering fabric heat loss and ventilation heat loss (Correct answer)
- Estimating 1kW per radiator regardless of room size
- Using only the floor area multiplied by a fixed factor
Correct answer: Using the U-value method considering fabric heat loss and ventilation heat loss
The correct method involves calculating total heat loss from the room, including fabric heat loss through walls, windows, floor, and ceiling using U-values, areas, and temperature differences, plus ventilation heat loss based on air changes per hour and room volume. The radiator output must match the total calculated heat loss.
Question 6: What is the correct procedure for pressure testing a new central heating system before commissioning?
- Run the system at operating temperature for 1 hour
- Fill the system and check for visible leaks only
- Pressurise the system to 1.5 times the maximum working pressure for a minimum test duration, checking for pressure drop (Correct answer)
- Test at normal operating pressure for 10 minutes
Correct answer: Pressurise the system to 1.5 times the maximum working pressure for a minimum test duration, checking for pressure drop
A new central heating system should be pressure tested at 1.5 times the maximum working pressure, or a minimum of 3 bar for sealed systems, for a defined test period. The system should hold pressure with no detectable drop and all joints should be visually inspected.
CENWAT Pipework Sizing and Installation 2
What type of fitting is NOT permitted for making joints on gas pipework concealed within walls?