CENWAT Boiler Types 1 — Questions and Answers
Question 1: What is the defining characteristic of a combination (combi) boiler?
- It provides both central heating and instantaneous domestic hot water from one unit with no separate hot water cylinder (Correct answer)
- It combines gas and oil firing
- It uses two heat exchangers for redundancy
- It combines floor-standing and wall-hung designs
Correct answer: It provides both central heating and instantaneous domestic hot water from one unit with no separate hot water cylinder
A combi boiler heats water directly from the mains for domestic hot water on demand and also provides central heating, eliminating the need for a separate hot water storage cylinder.
Question 2: What type of boiler requires a cold water storage cistern and a hot water storage cylinder?
- Conventional (regular/heat-only) boiler (Correct answer)
- Combi boiler
- System boiler
- Condensing boiler
Correct answer: Conventional (regular/heat-only) boiler
A conventional (regular or heat-only) boiler requires a separate cold water storage cistern in the loft and a hot water cylinder, making it suitable for properties with existing traditional systems.
Question 3: What is a system boiler?
- A boiler with the pump, expansion vessel and safety devices built in, requiring only a hot water cylinder (Correct answer)
- A boiler that heats only the central heating circuit
- A boiler with a built-in hot water storage cylinder
- A boiler that works without any external controls
Correct answer: A boiler with the pump, expansion vessel and safety devices built in, requiring only a hot water cylinder
A system boiler has key system components (pump, expansion vessel, PRV) built in and requires only a separate unvented or vented hot water cylinder, simplifying installation.
Question 4: What is the primary efficiency advantage of a condensing boiler over a non-condensing boiler?
- It recovers latent heat from flue gases by condensing water vapour, achieving efficiencies above 90% (Correct answer)
- It uses a larger heat exchanger
- It burns gas at a lower pressure
- It has a smaller combustion chamber
Correct answer: It recovers latent heat from flue gases by condensing water vapour, achieving efficiencies above 90%
Condensing boilers use a secondary heat exchanger to extract latent heat from water vapour in the flue gases, which would otherwise be wasted, achieving seasonal efficiencies above 90%.
Question 5: Since April 2005, what type of boiler is required by UK Building Regulations for new installations and like-for-like replacements?
- Condensing boiler (Correct answer)
- Any gas boiler above 70% efficiency
- Non-condensing boiler
- Back boiler
Correct answer: Condensing boiler
Since April 2005, Building Regulations Part L have required that replacement and new gas boilers in England and Wales must be condensing boilers, with very limited exceptions.
Question 6: What is the typical seasonal efficiency (SEDBUK) of a modern A-rated condensing combi boiler?
- 90% or above (Correct answer)
- 75–80%
- 60–70%
- 50–60%
Correct answer: 90% or above
Modern A-rated condensing combi boilers typically achieve SEDBUK efficiencies of 90% or above, compared to older non-condensing boilers which may be as low as 60–70%.
CENWAT Boiler Types 1
What is the defining characteristic of a combination (combi) boiler?