Bosch Therm 520 HN/520 PN 
Tankless Water Heater
Review and Buying Tips

A review of Bosch Therm 520 HN and Therm 520 PN, great compact tankless water heaters for smaller families and homes with one to two baths. Check out which model does not require electricity for power and why.

Features and specifications

Bosch Therm 520 tankless water heater

Bosch Therm 520 is the standard non-condensing type of tankless water heaters, similar to the discontinued models from the Aquastar 1600 series.

Bosch Therm 520 HN and 520 PN are similar units, they both use a simple venting system, using natural draft to remove the products of combustion in indoor residential applications. These models are built for budget-oriented families, and due to simple design, they don't utilize intelligent electronics and advanced features such as C 1210 ES, C 1050 ES, C 950 ES, and 940 ES models.

Bosch Therm 520 HN utilizes the patented hydro-power ignition while the 520 PN model piezo ignition system with the standing pilot, making both models independent of the electricity. The 520 PN uses the manual gas control slider to modulate the gas burner and adjust the temperature, while the 520 HN has two knobs for temperature adjustment, one that adjusts the gas supply and the other the water flow.

The main drawbacks are; the temperature control is from low to high - no temperature display; the models are not compatible with the wireless remote control and Intelligent Cascading, no Energy Star, and Low NOx compliance. The 520 series cannot be used in mobile homes, through heater recirculation, as the solar backup or a booster.


Both Therm 520 NH and 520 PN have an extended warranty of 15 years on the heat exchanger and 2 years on other elements.


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