CENWAT Water Heater Regulations 2 — Questions and Answers
Question 1: What document must be completed when commissioning an unvented hot water cylinder?
- Building Regulations Part G compliance notification and Benchmark commissioning checklist (Correct answer)
- Only the Gas Safe certificate
- Only the manufacturer's installation record
- Water company notification form only
Correct answer: Building Regulations Part G compliance notification and Benchmark commissioning checklist
Installation of an unvented hot water system is notifiable under Building Regulations Part G; the installer must notify the local authority (or use a Competent Person Scheme) and complete the Benchmark checklist.
Question 2: What temperature should an unvented cylinder thermostat be set to?
- 60–65°C (Correct answer)
- 40–45°C
- 80–90°C
- 50°C maximum
Correct answer: 60–65°C
The cylinder thermostat on an unvented unit is typically set to 60–65°C to ensure Legionella prevention while remaining safely below the thermal cut-out and T&P relief valve activation temperatures.
Question 3: What is the purpose of the temperature and pressure relief (T&P) valve on a water heater?
- To discharge hot water safely if the cylinder temperature or pressure exceeds safe limits (Correct answer)
- To balance pressure between hot and cold systems
- To regulate the temperature of the stored water
- To prevent cold water entering the hot system
Correct answer: To discharge hot water safely if the cylinder temperature or pressure exceeds safe limits
The T&P relief valve is a critical safety device that opens automatically if the cylinder temperature or pressure rises to dangerous levels, discharging water to prevent explosion.
Question 4: Where must the discharge pipe from a T&P relief valve terminate?
- To a safe, visible point outside or to a tundish then to a drain, so discharge can be observed safely (Correct answer)
- Directly into the nearest drain inside the property
- Into the cold water storage cistern
- Back to the boiler return pipe
Correct answer: To a safe, visible point outside or to a tundish then to a drain, so discharge can be observed safely
The discharge pipe must terminate in a safe, visible location (typically outdoors) or via a tundish to a drain, so that any discharge is immediately apparent and does not cause harm or flooding.
Question 5: What is a tundish and why is it used with a T&P relief valve discharge pipe?
- An open funnel fitting that provides an air gap, acting as a backflow break and allowing discharge to be observed (Correct answer)
- A pressure-reducing fitting
- A type of expansion vessel
- A drain valve for the cylinder
Correct answer: An open funnel fitting that provides an air gap, acting as a backflow break and allowing discharge to be observed
A tundish is an open funnel with an air gap that connects the T&P valve discharge pipe to the drain pipework. It prevents backflow contamination and makes discharge visible.
Question 6: What is the maximum storage temperature typically set for a domestic hot water cylinder to balance Legionella prevention against scalding risk?
- 60°C at the cylinder, with a TMV to blend down to safe outlet temperatures (Correct answer)
- 80°C to ensure rapid Legionella kill
- 45°C as a compromise
- 50°C with no TMV required
Correct answer: 60°C at the cylinder, with a TMV to blend down to safe outlet temperatures
The accepted approach is to store at 60°C (killing Legionella) and then fit a TMV at point of use to blend water down to safe outlet temperatures (43–48°C), addressing both risks.
CENWAT Water Heater Regulations 2
What document must be completed when commissioning an unvented hot water cylinder?