Vaillant combi boilers

Can I get hot water from a combi boiler?

Combi boilers are increasingly popular in UK homes and now make up over 50% of new boiler installations. They have a number of advantages over other types of boiler, and they really do offer instant hot water.

What exactly is a combi boiler, how does it work and what advantages does it have?

What is a combi boiler?

As the name suggests, a combi boiler combines a central heating boiler, and a water heater in one streamlined unit. They have two independent heat exchanges, one that links to your radiators, another that links to your hot water supply.

If the room thermostat falls below a certain temperature, the boiler will fire up enabling heat to be pumped into the central heating system. When the required temperature is reached, the boiler will adjust the heat levels by burning less fuel and saving energy.

When a tap is turned on, a valve in the boiler diverts the heat into the hot water supply. When the tap is turned off the valve returns to the central heating position.

How do combi boilers heat hot water?

Combi boilers take water from the mains and heat it on demand. When there’s no water demand, they remain on standby. This means they can heat water for your home without the need for a separate water tank and that hot water is always on tap whenever it’s required.  To produce hot water out of the taps the cold water passes across a highly efficient heat exchanger.  This heat exchanger transfers an incredible 90% of the heat from the burnt fuel to the water. Removing the need to store hot water in a tank means that heat isn’t lost in storage, making it a highly energy efficient way to heat water.

What are the pros and cons of combi boilers?


  • Greater efficiency – considerably more efficient than older boilers and could save you up to £300 a year on your heating bills.
  • Cheaper – they are simpler than alternative heating systems, meaning they cost less to install and maintain.
  • Faster – you have an unlimited supply of hot water immediately on tap.
  • More compact – as there’s no need for a separate water tank, combi boilers are a great choice where space is limited.
  • Less likely to suffer from pressure issues – as the water is taken directly from the mains, combi boilers are less likely to suffer from air locks or low pressure.
  • Easier to service- combi boilers are simpler to maintain, and less prone to breakdown than other systems.


  • Dependent on mains pressure – for a combi boiler to work properly you need good mains pressure.
  • Single use – with a combi boiler you can’t run more than one bath or shower at a time or turn on a hot tap while someone is showering. This can make them impractical in larger homes and households.
  • No immersion heater – as there’s no hot water tank you cannot have an immersion heater. This means if your combi boiler breaks down, you’re left without hot water as well as central heating.
  • Can’t be used with a power shower – as the water pressure is determined by the mains pressure, they are incompatible with power showers.

For more advice about combi boilers and whether they are appropriate for your property, contact us today.

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