Bosch Tankless Hot Water Heaters Review and Buying Tips

Write | Read Bosch tankless review

Explore the advantages and top features of Bosch tankless hot water heaters, including the most innovative models and top sellers. An expert review of gas and electric Bosch water heaters, including popular series; Therm, Greentherm from gas and Tronic from the electric group, all designed for on-demand heating of potable water in residential and light commercial applications.

As the water heating is the second largest energy user in one household, buying the energy-efficient, or even better – Energy Star unit, is the way to go for the homeowners. And this is where buying a Bosch tankless comes in place.

Why Bosch

Bosch manufacturer offers an endless hot water on demand, reduced energy consumption and savings on heating cost up to 50%, also space saving and reduced gas emission. And by buying the condensing unit, with the efficiency of over 90%, savings are even greater.

Note: the latest models built by Bosch and released in 2017, Greentherm 9000 series, could achieve the “industry highest” energy factor of 0.99 and thermal efficiency of 100%.

Also, let’s not forget, that the average life expectancy of the Bosch tankless is over 20 years, the warranty is 15 years while offering some amazing features such as the innovative technology and advanced electronics that provides stable and accurate temperature and diagnostics.

Bosch is a German manufacturer of HVAC products for residential and commercial applications, building quality products from 1886. In North America, you can find several brands in the tankless category, as mentioned above, while in Europe, Bosch tankless hot water heaters are known as Junkers. Popular Aquastar and Powerstar models are discontinued and these got replaced by the Therm, Greentherm and Tronic brands.

When comparing to the old Aquastar and Powerstar, new Greentherm and Therm series are much more advanced, safer, reliable and durable, and with the greater energy savings.

Tankless advantage

Tankless heat water on demand and saves up to 50 % on heating costs. For those homeowners who prefer fresh water always, available any time and in an endless supply, the tankless is the solution. This type saves money by not heating the stored water and when there is no demand, so there is no standby energy loss. You don’t have to wait for the water tank to fill up and then heat and then deliver. With the tankless, hot water is heated directly and is available almost immediately. As some will complain that the flow rate is limited, some manufacturers offer a solution by linking two or more units into one system and therefore provide more hot water.

Also, if it takes longer for hot water to get to the tap, Bosch offers tankless models with the circulation pump built-in, and recirculation system.

Even if they fail, with the 100% serviceable parts, you can replace the malfunctioning component instead of through it out on the landfill, as it would happen with the tank-type model, if for example is leaking.

Yes, they cost more than the conventional type, but they last longer, have lower operating and energy costs, are more convenient to use, provide enhanced comfort, and overall experience is better.

Bosch gas tankless review

Best features

Both Therm and Greentherm group of gas tankless water heaters come with the built-in digital control panel that allows not only monitoring the temperature rise but programming with the precise temperature adjustment and safety control.

Also, thanks to the dual fan, modulating vertical burner and built-in turbulators, the units can operate more efficiently and last longer, due to the reduced scale build-up.

For homes with the high hot water demand, or commercial applications, up to 24 models (some models), either Therm or Greentherm can be linked together in cascades.

All the models are compact, lightweight and wall-mounted which makes them easy to handle and install, saving the floor space for other use.

Bosch Therm series review

Therm series

Bosch Therm series is the newer line of the advanced condensing and non-condensing tankless water heaters that come with the energy factor that can reach high 98% and very small amount of heat loss (around 2%).

Our focus will be on water heaters for residential use. Most of the models are non-condensing and they come with the power range from 74,900 to 199,000 BTU and efficiency up to 83%, while there are only three condensing models whose power is from 175,000 to 225,000 BTU and thermal efficiency up to 98%. Some models with the reviews are shown in the list below and via the appropriate links.

Therm condensing models are Low NOx and Energy Star approved. In the residential application, they can heat water up to 140 F, while in commercial up to 184 F. The smallest models, such as 330 and 520 series) are very simple; they are equipped with the piezo ignition and high-to-low temperature option.

Model C 1210 ES, which is reviewed here in details, is the largest and most advanced model (flow rate of 12.1 GPM) that can also deliver more hot water to demanding applications due to its flexibility to work in the Cascade setup and with other model types (solar and electric).

Bosch Greentherm series review

Bosch Greentherm models are tankless and condensing gas water heaters that are operating with the ultra-high thermal efficiency of over 94% and utilize several innovative features such as the modulating gas valve, active bypass and intelligent electronics for the maximum performance, temperature stability and reliable operation. 

All the models, either installed indoor or outdoor are Low NOx and Energy Star compliant, which means the flexible installation, reduced pollution, and energy savings.

Due to the lower exhaust gases, Greentherm models are able to use PVC or PP vents, using the concentric setup.

The smaller Greentherm C 950 ES comes with the power of up to 175,000 BTU and water flow of 9.2 GPM (35 F rise) and larger Greentherm C 1050 ES with the power of up to 199,000 BTU and flow rate of 10.5 GPM (35 F rise).

Both models come with a warranty of 15 years.

Bosch electric tankless review

Bosch Tronic

Bosch Tronic

Bosch Tronic is the series of the small electric tankless water heaters designed for the whole house and point-of-use applications – mainly smaller homes, apartments, and cottages. 

The largest model provides endless hot water up to 3 major applications. Even designed small and compact, they are powerful and efficient that can be installed virtually anywhere inside the home.

There are three models available, first two are tankless and the last one is tank-type:

  • Tronic 6000/5000 – available in three sizes (WH36, WH27, and WH17) all for the whole-house application

  • Tronic 3000 – available in five sizes from US3 to US12 and are known as under-sink models

  • Tronic 3000T – available in three sizes ES2.5, ES4 and ES8 and are known as POU or point of use models

The largest electric model WH36, with its 36 kW of power is able to provide endless hot water to up to 3 major applications. Designed small, lightweight (26.5 lbs) and compact, they can be installed virtually anywhere inside the house, and due to its powerful and efficient operation, they can be used in whole-house applications.

The warranty is 5 years.


All of the Bosch tankless water heaters no matter power by gas or electricity, with its advanced features and latest technology, are providing superior water heating, while saving the valuable floor space for other use, lower the energy cost and provide the ultimate comfort with an endless supply of hot water. Due to the tankless design and with the built-in modulation, they ensure the constant temperature and enhanced comfort. Mini tanks on the other side are mainly for point-of-use applications, as they produce a small volume of hot water.

Review, Ask or Comment

And what do you think about Bosch?

What Other Visitors Have Said

Click below to see contributions from other visitors to this page...

Installing Bosch tankless water heater flue 
Here's a story from the great Canadian north. I live in Alberta where winter can be severe. About 10 years ago, I had a tankless Bosch water heater installed …

Bosch Power Star model 45-557701 
I had this model tankless water heater installed in my home in 2008. It was the Bosch Power Star model. Within two months it stopped heating water. Bosch …

Bosch 520 doesn't produce hot water 
Hi, I live in Montreal, Canada and I just bought the house with the Bosch tankless water heater, model 520 installed, which uses the hydro generator feature. …

Why my Bosch tankless WH freezes during winter 
What do I have to do to protect my Bosch water heater from freezing during the winter time. I have try to winterize it but obviously I am missing something. …

Bosch 2400E Not rated yet
My Bosch 2400E NG is 10 years old and all of a sudden it had a pinpoint leak in the heat exchanger. I live in the south so it has never frozen. The leak …

Click here to write your own.


Pictures are courtesy of Bosch company

Home > Bosch water heaters

water heaters

fireplace gas line