Bosch Therm C 1210 ES 
Tankless Water Heater
Review and Buying Tips

Explore the best from Bosch - Therm C 1210 ES, a tankless and condensing water heater. Check out the detailed review of the top features, including the powerful and green gas burner, high efficiency, low gas emission and increased flow rate for the high demanding applications.


Models overview

Bosch C 1210 ES tankless water heaterBosch C 1210 ES

The Bosch Therm C 1210 ES model was built as the condensing water heater that heats water on demand and supplies hot water in endless supply, with the ultra-high thermal efficiency and flow rate. Due to its innovative design, Bosch tankless heaters can easily compete with other brands such as Noritz, Rinnai, and Takagi.

Bosch tankless and condensing models use natural or propane gas for heating water directly, and flue gases to heat the incoming cold water indirectly, resulting in the lower temperature of exhaust gases. This allows usage of PVC vents, instead of more expensive stainless steel.

High energy efficiency of 98% means that only a few percent of the heat are lost, while most of the energy goes toward heating the cold water. High performance also means lower emission and less pollution. Since the model was designed with the gas input of 225,000 Btu, it is not Energy Star certified (to be eligible for ES program, the maximum power should be 199,900 Btu or less), but it can heat and provide lots of hot water, reaching high 12.1 gallons per minute.

This model is also ASME certified, which ensures the high quality of materials and craftsmanship; and with the superior design Bosch can provide long 15-year warranty, which is longer the warranty than on most models from other manufacturers (12-year is the maximum).


Easy installation

All tankless water heaters from Bosch, including the Therm C 1210 ES are designed compact and small, which allows easy handling, flexible wall-mount installation, and with the sealed combustion chamber, installation almost anywhere inside your home.

As most of the modern tankless water heaters, Bosch Therm C 1210 ES does not use the pilot light to light the main burner but the electrode and electronic ignition. When the main burner is lit, thanks to its innovative design, the maximum heat energy goes toward heating the water in the first heat exchanger, while the lost energy in the flue gases heats the incoming water in the second, aluminum heat exchanger.

Venting options

The flue gases are further taken out through the direct vent system, installed either horizontally or vertically in a concentric or twin pipe configuration, using the PVC, PP, ABS and CPVC vents and with the maximum pipe lengths of 63 feet.

Bosch Therm C 1210 ES is available as the indoor and outdoor model (with the optional outdoor kit), which gives more flexibility during the installation.

Power adjustment

Modulating gas valve and its constant gas/air ratio control makes the water heater work in the range from the minimum gas input of 25,000 to the maximum of 225,000 BTU, including the applications with the variable water flow. Also, with the modulating water valve, the comfort increases while the temperature control improves.

The Bosch C 1210 ES models are approved for combined domestic water and space heater, but only in the open-loop setup, and not in close-loop space heating applications. Keep in mind that the warranty is reduced to 3 years.

The recirculation through the unit is allowed, and when combined with the small mini-tank such as Tronic 3000 T, hot water is delivered faster with less waiting, the temperature stability is improved and overall customer satisfaction.

High water flow

It was said that this Bosch condensing water heater provides high 12.1 GPM which is enough for large homes with up to five showers. If there is a need for even more hot water, the Intelligent Cascading system allows connecting up to 24 units into the one system.


At the front of the unit, there is a control panel with the LCD display that shows the temperature, few indicators and error codes, for easy troubleshooting, ON/OFF and program/temperature control buttons.

As the system comes with the real-time diagnostics users can take advantage not only for the informational purposes but for troubleshooting and faster repair. The wireless remote is optional and is used to control the temperature of the outgoing hot water.

Safety features

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

Related: High-end model - Rinnai RUR98


  • Power: 25,000-225,000 BTU
  • Maximum water flow: 12.1 GPM
  • Thermal efficiency: 98%
  • Temperature range: 100-140 F (commercial C 1210 ESC models can reach up to 180 F)
  • Accuracy: +/- 2 F
  • Maximum exhaust and combustion air pipe lengths - 63 ft. for the twin pipe system or 43 ft. for a concentric setup
  • Vent size: 3 or 4 inch
  • Maximum altitude 8,000 ft.
  • Minimum water flow to activate: 0.5 GPM
  • Water pressure: min 30, max 145 PSI
  • Size: 11” X 18” X 30.5”, Weight: 74 lbs
  • Warranty 15 years on heat exchangers

Note: The C 1210 ES is not designed for installation in mobile (manufactured) homes.

Bosch Therm C 1210 ES is a powerful tankless water heater that is designed not only for heating potable water at home but for space heating as well, also for recirculation and instant hot water delivery and as the back-up in solar water heating. That is why a tankless from Bosch is a good buy.


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