Теплоноситель находится в системе.

Теплоноситель means heat carrier or heat-transfer medium—for example, a liquid or substance that carries heat through a heating system.

It is made from:

• тепло- = heat
• носитель = carrier, bearer, something that carries

So the word is very literal: something that carries heat.

Теплоноситель is in the nominative singular because it is the subject of the sentence—the thing that is located somewhere.

Russian dictionary form:

• теплоноситель = nominative singular

In this sentence, it answers the question what is located in the system? → теплоноситель.

Находится means is located, is situated, or simply is found.

It comes from the verb находиться, which is commonly used when talking about location:

• Книга находится на столе. = The book is on the table.
• Офис находится в центре. = The office is in the center.

In this sentence, находится sounds a bit more formal or technical than just expressing location in a simpler way.

In the present tense, Russian often leaves out to be:

• Книга на столе. = The book is on the table.

So technically, a shorter version like:

• Теплоноситель в системе. could work in some contexts.

But находится is used because it is more explicit and more natural in formal, technical, scientific, or written language. It emphasizes location:

• The heat-transfer medium is located in the system.

Because the preposition в is being used to show location (in), and with location it normally takes the prepositional case.

So:

• система → nominative
• в системе → prepositional

This answers where?

• Где находится теплоноситель? = Where is the heat-transfer medium located?
• В системе. = In the system.

In Russian, в can mean both in and into, depending on the case:

• в + prepositional = in / location
• в + accusative = into / movement toward

Here we have:

• в системе → prepositional so it means in the system, not into the system.

Compare:

• Теплоноситель находится в системе. = The heat-transfer medium is in the system.
• Теплоноситель поступает в систему. = The heat-transfer medium enters the system.

Системе is the prepositional singular form of система.

Declension:

• nominative: система
• genitive: системы
• dative: системе
• accusative: систему
• instrumental: системой
• prepositional: системе

After в meaning in, Russian uses the prepositional, so:

• в системе = in the system

Yes. Russian word order is flexible, although the neutral order here is:

• Теплоноситель находится в системе.

You could also say:

• В системе находится теплоноситель.

This version puts more focus on where it is.

In technical writing, both are possible, but the original sentence sounds neutral and straightforward.

Yes. Находится is 3rd person singular, matching the singular subject теплоноситель.

Compare:

• Теплоноситель находится в системе. = singular
• Теплоносители находятся в системе. = plural

So the verb agrees with the subject in number.

Yes, it sounds fairly formal, technical, or informational.

That is mainly because of:

• the technical noun теплоноситель
• the verb находится, which is common in formal descriptions

In everyday speech, people often use simpler structures, but in manuals, engineering texts, and technical explanations, this sentence sounds very natural.

It is possible, but it usually means something slightly different.

• Теплоноситель находится в системе. = The heat-transfer medium is located in the system.
• В системе есть теплоноситель. = There is a heat-transfer medium in the system.

The version with есть emphasizes existence/presence, while находится emphasizes location. In technical context, находится is often the better match for is located.

It most naturally answers:

• Где находится теплоноситель? = Where is the heat-transfer medium?

Answer:

• Теплоноситель находится в системе.

This is a useful way to understand the grammar:

• теплоноситель = what?
• находится = is located
• в системе = where?