CENWAT Boiler Types

Question 1

What is the defining characteristic of a combination (combi) boiler?

Accepted Answer

It provides both central heating and instantaneous domestic hot water from one unit with no separate hot water cylinder

Answer

It combines gas and oil firing

Answer

It uses two heat exchangers for redundancy

Answer

It combines floor-standing and wall-hung designs

Question 2

What type of boiler requires a cold water storage cistern and a hot water storage cylinder?

Accepted Answer

Conventional (regular/heat-only) boiler

Answer

Combi boiler

Answer

System boiler

Answer

Condensing boiler

Question 3

What is a system boiler?

Accepted Answer

A boiler with the pump, expansion vessel and safety devices built in, requiring only a hot water cylinder

Answer

A boiler that heats only the central heating circuit

Answer

A boiler with a built-in hot water storage cylinder

Answer

A boiler that works without any external controls

Question 4

What is the primary efficiency advantage of a condensing boiler over a non-condensing boiler?

Accepted Answer

It recovers latent heat from flue gases by condensing water vapour, achieving efficiencies above 90%

Answer

It uses a larger heat exchanger

Answer

It burns gas at a lower pressure

Answer

It has a smaller combustion chamber

Question 5

Since April 2005, what type of boiler is required by UK Building Regulations for new installations and like-for-like replacements?

Accepted Answer

Condensing boiler

Answer

Any gas boiler above 70% efficiency

Answer

Non-condensing boiler

Answer

Back boiler

Question 6

What is the typical seasonal efficiency (SEDBUK) of a modern A-rated condensing combi boiler?

Accepted Answer

90% or above

Answer

75–80%

Answer

60–70%

Answer

50–60%