Bosch Therm 940 ES
Tankless Water Heater
Review and Buying Tips

An overview of the Bosch Therm 940 ES model, the largest non-condensing tankless water heater from Bosch, recommended for 4-bath homes.

Features and specifications

Bosch 940 ES is the standard type tankless water heater designed as the direct vent unit with a gas-sealed combustion chamber for safe use inside the house. With the right venting kit, it can be installed outdoors too.

Its powerful and Low NOx burner and one long-lasting copper heat exchanger can generate lots of power, resulting in a high energy factor of 0.83, making it Energy Star compliant. Bosch 940 ES is the whole-house water heater where its maximum water flow rate of 9.4 gallons per minute makes it ideal for larger families as up to four simultaneous showers can be used. Also, the minimum water flow of 3 gallons makes the usage also convenient where a smaller amount of hot water is needed.

Bosch Therm 940 ES model is approved for domestic hot water recirculation applications, so you can get hot water faster than if the circulation pump is not used.

This tankless model can also be paired with the storage tank and Ariston mini-tank Tronic, where more hot water is needed while the wait time is reduced. One tankless unit might not be enough for larger homes and high-demanding applications, so the recommendation is to use the Intelligent Cascading Kit so up to 24 units can be connected into one system to generate more hot water.

The water heater can also be combined with the solar water heater system if the solar panels cannot provide enough hot water, the gas tankless acts as the booster.

The advanced electronics allow gas and water valve modulation, so the power, based on the water needs, adjusts automatically from 19,900 to 199,000 BTU. Another great advantage is the real-time diagnostic represented by the failure codes on the LCD display, which makes the problem diagnostic and repair easy. 

As seen from the above technical data and when compared to other non-condensing models, Bosch Therm 940 ES is the most powerful non-condensing tankless water heater that produces the highest water flow of all conventional tankless water heaters from Bosch. Due to the innovative design, the water heater can run on natural or liquid propane gas, while its small and compact design ensures flexible installation and wall-mounted inside or outside the residential house, commercial office, even the mobile homes.

Safety features

  • Built-in freeze protection inside the heater, down to 5 F but only for the short-term conditions
  • ECO protection against overheating
  • Flame failure device (ionization flame rod sensor)
  • Outlet temperature sensor
  • Backflow temperature sensor
  • Flue temperature sensor
  • Water drop protection
  • Condensate drain


  • Power: 19,900-199,000 BTU
  • Maximum water flow: 9.4 GPM
  • Thermal efficiency: 83%
  • Temperature range: 100-140 F (commercial C 950 ESC models can reach up to 180 F)
  • Accuracy: +/- 2 F
  • Maximum exhaust and combustion air pipe lengths - 63 ft. for twin pipe system or 43 ft. for concentric
  • Vent size: 3 or 4 inch
  • Maximum altitude 8,000 ft.
  • Minimum water flow to activate the unit: 0.5 GPM
  • Water pressure: min 30, max 145 PSI
  • Size: 11” X 18” X 30.5”, Weight: 67 lbs


Bosch provides a long warranty of 15 years on the heat exchanger and 5 on other parts.


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