PLUMBING and HEATING INFORMATION - What is an Instantaneous Combi Boiler? - What are the Advantages of an Instantaneous Combi Boiler? - What are the Disadvantages of an Instantaneous Combi Boiler?

What is an Instantaneous Combi Boiler?

An instantaneous combi is a combination boiler that has little or no stored hot water.

What are the Advantages of an Instantaneous Combi Boiler?

The advantages of an instantaneous combi boiler are
1. There is no tank of stored cold water in the loft.
This may give a better usage of the loft space (but see below).
2. The instantaneous combi boiler only heats water as it is needed
and so it can be very energy efficient.

What are the Disadvantages of an Instantaneous Combi Boiler?

The disadvantages of an instantaneous combi boiler are
1. There is no tank of stored cold water in the loft.
If the mains water supply stops running due to maintenance
or a fault, then the property has no cold water.
2. The unstable flow rate through the boiler can be a problem for showers.
A thermostatic mixer shower is recommended for use with an instantaneous combi.
3. An instantaneous combi may not cope very well with supplying hot water to many
outlets in a property with lots of people. This is because the flow rate will drop
causing a poor showering experience or a long delay in filling a bath.
The temperature of the hot water may decrease if the boilers power (size) is insufficient.
In the past, an instantaneous combi boiler was usually used for flats or small houses
but today many larger houses are using a suitable storage combi.
4. The instantaneous combi and the storage combi both make a priority for hot water usage.
This means that when hot water is being used, the boiler stops heating the radiator circuit.
When the hot water stops being used, the boiler returns to heating the radiators.
This can be a problem if many people are using hot water for a long time
as the temperature of the property may start to decrease.

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