Boiler Types Flashcards

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

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.

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

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.

What is a system boiler?

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.

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

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%.

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

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.

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

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%.