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100+ Free C&G 6189 L3 Practice Questions

City & Guilds 6189 Level 3 NVQ Diploma in Domestic Plumbing & Heating practice questions are available now; exam metadata is being verified.

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2026 Statistics

Key Facts: C&G 6189 L3 Exam

100

Practice Questions

OpenExamPrep

Level 3

Competent-Craftsperson Diploma

City & Guilds

G3

Unvented Hot Water Competency

Building Regs Approved Document G

~90 deg C

Temperature Relief Valve Setting

Approved Document G3

55 deg C

Part L Design Flow Temperature

Approved Document L

5

Water Regs Fluid Categories

Water Fittings Regulations 1999

The City & Guilds 6189 Level 3 NVQ Diploma in Domestic Plumbing & Heating is the advanced, competent-craftsperson qualification for UK plumbers and heating engineers, awarded by City & Guilds through approved centres. It is assessed through per-unit online multiple-choice knowledge tests plus practical assignments and a work-based competence portfolio rather than a single timed exam, so question counts vary by unit. Content spans complex cold and hot water systems, unvented hot water under Building Regulations G3 (expansion and safety devices, tundish and discharge pipework), central heating design and commissioning, electrical and control systems for heating, fault diagnosis and rectification, environmental and renewable technologies, and the Water Supply (Water Fittings) Regulations. This free prep includes 100 research-based practice questions with explanations and an AI tutor to drill the theory knowledge, with a strong emphasis on G3 unvented hot water.

Sample C&G 6189 L3 Practice Questions

Try these sample questions to test your C&G 6189 L3 exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Under Building Regulations Approved Document G3, which combination of in-line safety devices must protect a packaged unvented hot water storage cylinder against overheating and over-pressure?
A.A single check valve and a vacuum breaker
B.A pressure reducing valve, an expansion relief valve and a temperature relief valve
C.A double check valve and an anti-gravity loop
D.A motorised valve and a programmable thermostat
Explanation: G3 requires layered protection. The pressure reducing (or pressure-limiting) valve controls inlet pressure, the expansion relief valve protects against over-pressure, and the temperature relief valve (a separate thermostatically operated valve) protects against overheating by dumping water before it can flash to steam. These are the mandatory non-self-resetting safety controls.
2At approximately what temperature is the temperature relief valve on a G3 unvented hot water cylinder set to operate?
A.60 degrees C
B.70 degrees C
C.90 degrees C
D.120 degrees C
Explanation: The temperature relief valve is factory set to open at approximately 90 to 95 degrees C. This discharges scalding water to the tundish and drain before the stored water can reach 100 degrees C and flash to steam, which is the principal explosion hazard the G3 controls guard against.
3On an unvented hot water installation, where must the tundish be positioned in relation to the temperature relief valve?
A.At least 2 metres below the valve
B.Within 500 mm of the valve and in a visible position
C.Immediately at the drain connection regardless of distance
D.Inside the cylinder cupboard out of sight
Explanation: G3 guidance requires the tundish to be fitted within 500 mm of the safety valve and in a position where any discharge will be visible to the householder, alerting them to a fault. The tundish provides the visible air break (type AUK) between the safety valve and the foul drain.
4The discharge pipe D2 (downstream of the tundish) on an unvented system must be laid to which minimum continuous fall?
A.1 in 10
B.1 in 40
C.1 in 200
D.Level, with no fall required
Explanation: Approved Document G3 requires the D2 discharge pipe from the tundish to have a continuous fall of at least 1 in 200 so that discharged water drains away under gravity and cannot pond. The first vertical section below the tundish must also be at least 300 mm before any elbow or bend.
5Which body of water expansion must the expansion vessel or expansion volume accommodate on a sealed unvented hot water cylinder?
A.The expansion of the central heating water only
B.Approximately 4% of the stored hot water volume as it is heated
C.The full cylinder volume in case of total drain-down
D.The cold mains supply pressure surge only
Explanation: Water expands by roughly 4% when heated from cold (about 10 degrees C) to 65 degrees C. On a sealed unvented system this expansion must be taken up by an expansion vessel or an integral air gap so that pressure does not rise to the expansion-relief setting during every heat-up cycle.
6What is the principal function of the pressure reducing valve fitted on the cold feed to an unvented cylinder?
A.To raise incoming mains pressure to the cylinder rating
B.To limit and stabilise the inlet pressure to the value the cylinder is designed for
C.To prevent legionella growth in the stored water
D.To act as the final overheat cut-out
Explanation: The pressure reducing (pressure-limiting) valve sets a controlled, stable inlet pressure, commonly around 3 bar, matching the cylinder and its expansion/relief settings. This ensures the expansion relief valve only lifts on a genuine fault, not on normal mains fluctuation.
7Which legal notification is required before an unvented hot water storage system over 15 litres is installed in a dwelling?
A.No notification is ever required
B.Notification to the local water undertaker only
C.Building Regulations notification, satisfied by using a registered competent person or notifying Building Control
D.Notification to the Health and Safety Executive
Explanation: Installing an unvented system over 15 litres is controlled work under G3. It must be notified through Building Regulations, which is normally satisfied by a G3-qualified installer registered with a competent person scheme self-certifying, or by direct notification to Local Authority Building Control.
8Why must the temperature relief valve on an unvented cylinder be located directly on the cylinder rather than on a connecting pipe?
A.To make annual servicing quicker
B.So its sensing element is directly in contact with the stored water at the hottest point
C.To reduce the cost of the discharge pipework
D.Because the expansion vessel cannot otherwise be fitted
Explanation: The temperature relief valve must sense the actual stored-water temperature, so it is mounted directly into the top of the cylinder where water is hottest, with its probe in the top 20% of the storage. Mounting it on a pipe could allow the stored water to overheat undetected if circulation stalls.
9A directly heated unvented cylinder uses which method to raise the stored water temperature?
A.An immersion heater or other heat source inside the cylinder itself
B.A primary heating coil fed by a boiler
C.A solar thermal coil only
D.Gravity circulation from a feed cistern
Explanation: A directly heated unvented cylinder heats the stored water with a heat source within the vessel, typically one or more electric immersion heaters. An indirect cylinder, by contrast, uses a primary coil fed by a boiler to transfer heat to the stored water.
10During servicing of an unvented cylinder, how should the charge pressure of an external expansion vessel be checked?
A.By weighing the vessel
B.With the system depressurised, using a tyre-type pressure gauge on the vessel's air valve
C.By measuring the hot water flow rate at the tap
D.By listening for water hammer
Explanation: The vessel air-charge must be checked with the water side isolated and drained to zero pressure, then a gauge is applied to the Schrader air valve. The charge should match the system's cold-fill pressure (commonly around 3 bar for unvented DHW). A vessel that has lost its charge cannot absorb expansion and will cause nuisance discharge.

About the C&G 6189 L3 Practice Questions

Verified exam format metadata for City & Guilds 6189 Level 3 NVQ Diploma in Domestic Plumbing & Heating is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.