Quando il tubo è libero, il termosifone smette finalmente di fare rumore.

Quando means when, not if. It suggests that the speaker sees this as something that does happen, or is expected to happen.

• Quando il tubo è libero = When the pipe is clear/free
• Se il tubo è libero = If the pipe is clear/free

So quando sounds more like a real or recurring situation, while se would sound more conditional or uncertain.

Literally, libero usually means free, but in this context it means something like:

• clear
• unblocked
• not obstructed

So il tubo è libero does not mean the pipe is free in some abstract sense. It means the pipe is clear/open, so whatever was causing the problem is no longer blocking it.

Also, libero agrees with tubo, which is masculine singular:

• tubo → masculine singular
• libero → masculine singular form

Italian usually uses essere for states and descriptions like this.

• è libero = is free / is clear

Using stare here would sound unnatural in standard Italian. Stare is often used for temporary conditions in some cases, but with an adjective like libero in this sentence, essere is the normal choice.

So:

• il tubo è libero = correct
• il tubo sta libero = not natural here

Italian uses definite articles more often than English does.

Here, il tubo and il termosifone mean:

• the pipe
• the radiator

Even when English might sometimes leave out an article or use a possessive, Italian often keeps the article. In this sentence, the speaker is referring to a specific pipe and a specific radiator understood from the context, so il is completely natural.

Termosifone is the common Italian word for a radiator used for home heating.

A native English speaker might expect a more direct equivalent of radiator, but in Italian everyday usage termosifone is very common. Depending on region and context, you may also hear other heating-related words, but termosifone is the standard everyday term here.

This uses a very common Italian pattern:

smettere di + infinitive

It means to stop doing something.

So:

• smette = (it) stops
• di fare = making / doing
• rumore = noise

Put together:

• smette di fare rumore = it stops making noise

Other examples:

• smettere di parlare = to stop talking
• smettere di fumare = to stop smoking
• smettere di piovere = to stop raining

Fare rumore is a very common Italian expression meaning to make noise.

Literally:

• fare = to do / to make
• rumore = noise

So the phrase works very much like English make noise.

Italian often prefers this simple expression in everyday speech. Even if a more specific verb could sometimes be used, fare rumore is the normal, natural choice here.

Italian often leaves out subject pronouns because the verb ending already shows the subject clearly.

Here:

• è = is
• smette = stops

The subject is understood from the noun:

• il tubo è libero
• il termosifone smette

You do not need to add a pronoun like esso. In fact, using esso would usually sound unnatural in ordinary speech.

This is different from English, where you normally must say it is or it stops.

Finalmente means finally, and its position is fairly flexible. In this sentence, it comes after smette and before di fare rumore:

• il termosifone smette finalmente di fare rumore

This is very natural and means:

• the radiator finally stops making noise

You could also hear:

• finalmente il termosifone smette di fare rumore
• il termosifone finalmente smette di fare rumore

These are all possible, but they may shift emphasis slightly. The version in your sentence sounds smooth and standard.

The present tense in Italian can describe:

• a general truth
• a habitual situation
• something that happens whenever a condition is met

So Quando il tubo è libero, il termosifone smette finalmente di fare rumore can mean something like:

• When the pipe is clear, the radiator finally stops making noise
• in the sense of this is what happens

Italian, like English, often uses the present for this kind of general relationship between two events.

The comma separates the quando clause from the main clause:

• Quando il tubo è libero, = dependent clause
• il termosifone smette finalmente di fare rumore. = main clause

This is very similar to English punctuation:

• When the pipe is clear, the radiator finally stops making noise.

The comma helps mark the pause and makes the sentence easier to read. In Italian, this is standard when the subordinate clause comes first.

Yes. In Italian, adjectives usually agree in gender and number with the noun they describe.

Here:

• tubo is masculine singular
• so the adjective is libero

Compare:

• il tubo libero = masculine singular
• la valvola libera = feminine singular
• i tubi liberi = masculine plural
• le valvole libere = feminine plural

This agreement is a very important part of Italian grammar.

Yes, Italian word order is flexible, though some versions are more natural than others.

Original:

• Quando il tubo è libero, il termosifone smette finalmente di fare rumore.

You could also say:

• Il termosifone smette finalmente di fare rumore quando il tubo è libero.

The meaning stays basically the same. The difference is mainly in focus:

• starting with Quando il tubo è libero emphasizes the condition first
• starting with Il termosifone smette... emphasizes the result first

Both are correct, but the original sentence is very natural if the speaker wants to highlight the condition.