Knowledge Center

Knowledge centre for Bosch and Junkers condensing boilers with instantaneous DHW heating – the differences between the GC2300iW, GC5700iW and GC8700iW ranges and what the CR/CT abbreviations in the model name mean.

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In the heating technology world, Bosch and Junkers are one and the same brand – Junkers was the original name under which Bosch condensing boilers were sold in some countries, and today they are unified under the single Bosch name. In this category you'll find Bosch condensing boilers with flow-through domestic hot water (DHW) heating – meaning without a built-in storage tank, the water is heated directly on demand.

Three Bosch Product Ranges by Output

Bosch groups its condensing boilers with flow-through heating into three output classes, distinguished by the GC designation and the range number:

GC2300iW 22/25 C – the entry-level range, a reliable and more affordable choice for a flat or a smaller house with one bathroom.
GC5700iW 20/30 C – a mid-range model with an output of 3.0 – 20.9 kW, available in white. Compared with the entry-level range, it offers a wider downward modulation range, meaning smoother control in milder weather.
GC8700iW 30/35 C – the most powerful range, with an output of 3.2 – 31.1 kW, designed for larger households or houses with higher heat losses, where the lower GC2300/GC5700 ranges may no longer have enough output reserve.

What the CR and CT Abbreviations in the Name Mean

With Bosch boilers, you'll often come across models with the abbreviation CR or CT plus a number added – these are pre-assembled packages that save time and the hassle of choosing compatible accessories:

+CR120 / +CR400 – a boiler bundled with an external hot water cylinder with a volume of 120 or 400 litres. Even though the boiler itself is designed for flow-through heating, connecting a cylinder gives you a hybrid solution with a larger, instantly available supply of hot water – useful if you're planning higher consumption in the future (for example an extra bathroom) without needing to replace the boiler itself.
+CT200 – a boiler bundled with the CT200 room thermostat for more comfortable and precise heating control based on room temperature.

If pure flow-through heating without a cylinder is enough for you, go for the base version of the boiler (e.g. GC2300iW 22/25 C) with no suffix. If you're considering higher hot water consumption in the future, it's worth looking straight at a package with a CR cylinder – it usually works out cheaper than buying a cylinder separately later.

Which Bosch Range to Choose

Flat or smaller house with one bathroom: GC2300iW 22/25 C, or the BASIC package with the CT200 room thermostat.
House with standard consumption, where you'll appreciate smoother control: GC5700iW 20/30 C.
Larger house or higher heat loss: GC8700iW 30/35 C, or straight away in a package with the CR400 external cylinder for higher hot water consumption.

When choosing the specific output, we also recommend following the general principles described in the Knowledge Center for boilers with flow-through heating – especially the section on maximum DHW flow rate by number of bathrooms. You'll find a wider range of condensing boilers from other brands in the Boilers with Flow-Through DHW Heating category.