CENWAT Central Heating System Design 3 — Questions and Answers
Question 1: What is the function of a thermostatic radiator valve (TRV)?
- To regulate the flow of water through the radiator based on room temperature (Correct answer)
- To act as the main system on/off control
- To measure system pressure
- To prevent water hammer in the pipework
Correct answer: To regulate the flow of water through the radiator based on room temperature
A TRV senses the air temperature around it and automatically adjusts the flow of hot water through the radiator to maintain the set room temperature.
Question 2: On which radiator should a TRV NOT normally be fitted in a wet central heating system?
- The radiator in the room where the room thermostat is located (Correct answer)
- Bedroom radiators
- Radiators in the hallway
- Radiators on the ground floor
Correct answer: The radiator in the room where the room thermostat is located
A TRV must not be fitted in the same room as the room thermostat, as both devices would compete for control, potentially causing the boiler to short-cycle or overheat.
Question 3: What is the purpose of a system filter (magnetic filter) in a central heating system?
- To capture magnetite and debris to protect the boiler heat exchanger (Correct answer)
- To remove dissolved gases from the water
- To filter the incoming gas supply
- To trap limescale before it enters the pump
Correct answer: To capture magnetite and debris to protect the boiler heat exchanger
A magnetic system filter captures iron oxide (magnetite) and other debris circulating in the system, preventing damage to the boiler heat exchanger and pump.
Question 4: What minimum efficiency is required for a new gas boiler installed in England under Building Regulations?
- 92% ErP (energy-related products) rating (Correct answer)
- 75% SEDBUK
- 80% net efficiency
- 65% gross efficiency
Correct answer: 92% ErP (energy-related products) rating
Under Building Regulations Part L, new gas boilers must meet a minimum ErP efficiency rating, currently requiring A-rated condensing boilers with around 92% seasonal efficiency.
Question 5: Which component prevents water from flowing backwards through the heating circuit?
- Non-return valve (check valve) (Correct answer)
- Pressure reducing valve
- Thermostatic mixing valve
- Zone valve
Correct answer: Non-return valve (check valve)
A non-return valve (check valve) allows water to flow in one direction only, preventing backflow which could cause mixing of circuits or system malfunction.
Question 6: What does the term 'dead leg' refer to in a hot water system?
- A section of pipework that does not circulate, causing water to cool (Correct answer)
- A pipe that has been decommissioned and capped
- A return pipe with no flow
- A bypass line around a valve
Correct answer: A section of pipework that does not circulate, causing water to cool
A dead leg is a length of pipe where water sits stagnant and cools between draw-offs. Long dead legs waste water and energy and can increase Legionella risk.
CENWAT Central Heating System Design 3
What is the function of a thermostatic radiator valve (TRV)?