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Bosch Therm 520 HN NG (Natural Gas) Whole-House Tankless Water Heater

3.6 out of 5 stars 11 customer reviews
| 13 answered questions

Price: $875.99 & FREE Shipping
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  • 117,000 max input (BTU)
  • 80% thermal efficiency
  • Patented Hydro-power ignition requires no electricity
  • Endless hot water for up to 2 applications at a time
  • Vents with galvanized B vent - natural draft
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Frequently Bought Together

  • Bosch Therm 520 HN NG (Natural Gas) Whole-House Tankless Water Heater
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Total price: $941.57
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Product Description

Product Description

The Therm 520 HN incorporates an evolutionary hydro-power ignition system which allows this tankless water heater to work without a standing pilot, grid connection or battery! A small turbine inside the water heater uses the energy from the flowing water to ignite the burner. The modulating gas valve then maintains a constant temperature at varying flow rates. This innovative technology, patented by Bosch, makes this an ideal product for installations without access to electricity or regions prone to inclement weather and power outages.

From the Manufacturer

The Therm 520 HN incorporates an evolutionary hydro-power ignition system which allows this tankless water heater to work without a standing pilot, grid connection or battery!

Product Information

Technical Details

Part Number Therm 520 HN NG
Item Weight 35 pounds
Product Dimensions 16.7 x 8.7 x 25.8 inches
California residents Click here for Proposition 65 warning
Item model number 520HNNG
Item Package Quantity 1
Usage Indoor
Batteries Included? No
Batteries Required? No

Additional Information

ASIN B0065OGB9Y
Customer Reviews
3.6 out of 5 stars 11 customer reviews

3.6 out of 5 stars
Best Sellers Rank #317,005 in Home Improvements (See top 100)
#358 in Home Improvement > Rough Plumbing > Water Heaters & Parts > Water Heaters
Shipping Weight 36 pounds (View shipping rates and policies)
Domestic Shipping This item is also available for shipping to select countries outside the U.S.
International Shipping This item is not eligible for international shipping. Learn More
Date First Available November 10, 2011

Warranty & Support

Manufacturer’s warranty can be requested from customer service. Click here to make a request to customer service.

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Customer Questions & Answers

Customer Reviews

Top Customer Reviews

We had this unit in our house for nine months before finally giving up on it. From the beginning, it was awful. It would randomly cut off when we were taking a shower, usually after about 2 minutes, leaving the water ice cold. We had the Bosch-certified technician who installed it back many times, and he couldn't figure out what was wrong. Eventually he was told by Bosch that we needed new mixing valves on the showers. As unlikely as it was that valves would fail on TWO different showers at the same time, we went ahead and spent $700 on plumbing repairs at the insistence of the Bosch folks. The result was the same cold showers. We had the city check our water pressure and change our meter. Still no good. We had a tech from Bosch look at it. No one could fix it.

Finally, we told the installer to take it out and put in a tank. Out installer is refunding us the installation and price of the unit. We are trying to get some redress from Bosch for the unnecessary plumbing work and two service calls.

The thing is a lemon. We have a Bosch oven, too, and we had to replace the same part on it twice in 5 years. No more Bosch products for us, ever.
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Excellent, however, somewhere in the instructions it should indicate that you have to put in a 1-inch gas line to feed it. We had to call the gas company for that information. Hooking it up to standard gas line makes it work only intermittently.
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I have the previous generation of this heater, and though I appreciate the engineering behind the hydro generated spark, the problems with Bosch and its design make it a poor choice. The largest problem is Bosch's technical support. Though many problems have surfaced with my heater- I've not been able to successfully claim any warranty work. The design is not freeze-area safe. Though it has resistive heaters to prevent icing on some parts of the unit, it just takes something not protected- in this case the water valve- to render the unit useless. The unit relies too heavily on plastic parts- both the hydro-generating unit and water valve housing are plastic. These cannot be heated and therefore freeze. Finding an official Bosch approved plumber is futile, as though I live in a metropolitan area, the only approved plumber is several hours away.
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I replace the Aqua Star 125 with this unit. Everything in place and the vent dimension is the same at 5". Easy install with 2 person. The unit initially not come up until we have to turn the Gas valse up side down since there no arrow to show which direction it should face. Overall, it a good product, I call tech support and they are very helpful.
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By JAW on December 27, 2014
I, too, have this model and live in MA. I agree with the RI customer but the shut off events are even more random. The heater works fine in the late spring, summer and early fall. Beyond that, we get random shut offs. We were told that it was the gas pressure -- gas company disagreed. In fact, they had indicated that we could have several more gas appliances and all should work. This model replaced our Aquastar that we had for 25 years with only two service calls. Since Bosch bought Aquastar we thought that we would have the same experience. Clearly we did not. We would not recommend this product.
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By Brad on September 25, 2015
Verified Purchase
This is the second time we have bought this product and we are very happy with the performance. We use it in an industrial setting and it preformed for 6yrs before we had to replace it. For the cost I would recommend it.
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