Bosch Gas Tankless Water Heater Reviews: Therm 520PN LP

With the many available Bosch gas tankless water heater reviews online, there is no doubt that this German company has earned its reputation by providing people all over the world with their top-notch products. Initially, the company’s expertise was related to the production of automotive components Later on, they included household appliances ranging from basic kitchen appliances (such as microwaves, coffee machines, dishwashers, etc.) to advanced home appliances (such as washing machines, ovens, water heaters, etc.)

We had a chance to take a closer look at one of the water heating units from their Therm series. The Therm series includes models that range from low-budget to extremely expensive ones. In this article, we will be focusing on Therm 520 PN LP model.

In that regard, we would like to present to you our very personal opinion and address why is this particular model is one of our favorite.

Before we start talking about the unit and what it does, it’s worth pointing out what it is. There are multiple variations of water heater units out there which are usually made in respect to the design of the building. However, we can say that they essentially boil down to two main categories: the tankless water heaters and the conventional gas-based heaters. 

These tankless heaters possess instantaneous and continuous flow of the water. Their innovative design allows immediate change of temperature in water as it runs through the heater unit. They do not contain and store any water internally except what’s currently cycling through its system. In comparison to standard gas-based heaters, tankless heaters can save up energy provided that certain conditions have been met.

For example, tankless water heaters are suitable for people who live in a place where power shortages frequently occur. Furthermore, it can also serve as a good addition to your house if electricity is scarce where you live. This way it can only heat water when it is in demand (when you open the water tap).

The way it works is that it doesn’t require any batteries or electricity. Instead, it powers on by utilizing a crystal which creates a spark onto the pilot light (Piezo ignition system). There is a knob switch on the unit which controls this action and makes it extremely convenient and user-friendly. However, if electricity is not a problem for you, check out this article on the best electric water heater in the market today.

Immediately after you turn off the water tap, the whole system shuts down as it detects the absence of the flow. One thing that is characteristic of these types of water heaters is that they do not deliver hot water almost instantly. If this is something that bothers you, you can rectify the issue by installing a recirculation pump.

Bosch Gas Tankless Water Heater Reviews [Model 520PN LP] - Features and Specifications

Energy Efficiency and Flow Rate

Bosch Therm 520 PN LP is one of the units from their newer line of tankless water heaters. Its design ensures that the water temperature remains constant throughout the whole heating process. It features Piezo push-button ignition system (which does not require an electric output) and operates at about 78% of thermal efficiency.

Moreover, the unit’s maximum input per hour equals to 117,000 of British Thermal Units (BTU) while its minimal is about 30,000 British Thermal Units. Its activation flow rate requirement equals to 0.5 GPM in order to offer you the ability to control the temperature from low to high. It uses a gas control slider which requires manual operation in order to control the gas burner and adjust the temperature levels.


As we inspected the unit, we noticed that it can actually maintain a temperature of 35F degrees rise while it operates with up to 5 gallons of water per minute. To our surprise, it justifies all the statements in the specification tab on the company’s website. Another thing that we noticed is that Bosch Therm 520 PN LP can simultaneously provide two water supplies with hot water (but not more than that).

Weight and Dimension

As far as its installation goes, we think that it’s relatively simple. Just follow what you see in the instruction manual, and you’ll be good to go. Bosch Therm 520 PN LP has been designed to be used exclusively in the interiors. Its weight is around 35 pounds while Its dimensions are 8.7’’ x  16.7’’ x 25.8’’, which elevates its compactness aspect to good levels.

Since it’s an indoor model, you are only limited to wall mount installation due to its design. This, however, can be a good thing as it allows for various venting possibilities. Venting is possible either through a natural draft or a galvanized B vent. Have in mind that the location where you install it can influence the flow of the water, which comes as one of the downsides of this unit. 


When it comes to its price, it’s just about there between the middle and the upper part of the price range (about $2,200 currently on Amazon). Since most propane tankless water heating units cost much more than that, we think that this is an ideal price. It’s not up there with the best, but it’s not supposed to be there in the first place. If you are looking for cheaper alternatives, click here.


Also, we want to mention that Bosch does a wonderful job by backing up most of their products with warranties that lead up to 15 years. They also ensure that their units’ serviceability is always at 100%, which boosts our impression about their customer support even more.

Pros and Cons

Everything that we’ve said so far might come to you as a lot to take in. With that in mind, we provide you with a short list of the unit’s pros and cons.


  • The unit can deliver hot water almost instantaneously
  • It does not require a power source or batteries in order to operate (it uses its own ignition system)
  • Its flow rate is minimal


  • The unit’s price might not be suitable for everyone
  • The flow rate of the unit depends entirely on where it has been installed
  • Even though its dimensions are pretty compact, the same can not be said for its weight (it’s a potential issue for some people because it’s ill-advised to install it high on the wall) 

Final Verdict

Bosch Therm 520PN LP Gas Water Heater

Bosch Gas Tankless Water Heater Reviews

Considering that this unit was built to be used exclusively in smaller residences for potable water heating, we think that its price matches the way it performs and what it has to offer. It’s extremely convenient for people who have multiple power fluctuations and constantly depend on the electricity. Bosch Therm 520 PN LP completely eliminates having to cover in fear and think whether your power’s gonna break or not. It’s completely independent and does not require anything other than its own system to operate.

Bosch really revolutionized their water heating products in a way that they are more focused on saving space and energy. On the other hand, Bosch products tend to be a little bit pricey in comparison to some other brands. If you are someone who likes Bosch products and is not concerned about the price, then we say go for it. However, if you want a unit that performs just as equally (or even underperforms) perhaps you should consider some other alternatives.

This review, like most other Bosch gas tankless water heater reviews, only serves to appropriate the product to the reader. We would like to emphasize the fact that we value individual opinion above everything else. After all, you are the one who is purchasing a product according to your preferences and needs.

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