What is a Combi Boiler?

Vaillant Combi Image

A combi (or combination boiler) is one that combines hot water production and space heating production into one package or appliance. It is commonly installed in properties where there is limited space for a separate hot water cylinder. Combi boilers have become highly prevalent in UK homes as hot water is generated instantaneously whereas in a seperate hot water cylinder setup, pre heated water may run out if the boiler is not able to heat up the hot water cylinder before it runs out due to high demand.

 

Advantages and Disadvantages / Pros and Cons of Combi Boilers

Advantages /Pros :

  • As long as the boiler is working, hot water will be continuously produced as long as necessary
  • Space saving
  • Mains pressured, so does not require booster pumps or Cold Water storage tanks unless there is problem with mains supply
  • Saves on installation cost and time

Disadvantages / Cons:

  • As the hot water is generated instanteously, should the boiler break down, there is no backup like an immersion heater that is found in seperate hot water cylinders.
  • More parts that can break down or get clogged up ie Divertor Valve, Plate Heat Exchanger, Filters etc. (Please not this is not the case on some advanced combi boilers that have 2 in 1 heat exchangers)
  • Limited flow rates so usually one bath or shower at a time (exceptions to this are Combis that have built in storage tanks)
  • Cannot be used by itself in conjuction with other renewable sources ie solar heating or heat pumps
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