De radiator heeft een thermostaat en een radiatorknop.

Radiator is a de-word in Dutch, so it takes the definite article de: de radiator.

Unfortunately, with many nouns, the article has to be learned along with the word. There is not always a simple rule you can rely on. Since radiator is a singular common-gender noun, de is correct.

Heeft is the third-person singular form of the verb hebben (to have).

The subject is de radiator, which is singular, so Dutch uses:

• ik heb
• jij hebt / heb jij
• hij/zij/het heeft
• de radiator heeft

So De radiator heeft ... means The radiator has ...

Een is the indefinite article, meaning a or an.

In this sentence, the radiator has:

• een thermostaat = a thermostat
• een radiatorknop = a radiator knob

Dutch uses een for both, regardless of whether English would use a or an.

Yes, radiatorknop is a compound noun, and Dutch forms these very often by writing the parts together as one word.

It is made up of:

• radiator = radiator
• knop = knob / dial / button

So radiatorknop literally means radiator knob.

This is very normal in Dutch. English often writes similar combinations as two words, but Dutch usually joins them.

This is normal main clause word order in Dutch:

subject + verb + rest

So here:

• De radiator = subject
• heeft = verb
• een thermostaat en een radiatorknop = object/complement

This is very similar to English:

• The radiator has a thermostat and a radiator knob.

Normally, Dutch repeats een here, so een thermostaat en een radiatorknop is the natural form.

If both nouns share the same article, Dutch sometimes omits repetition in certain contexts, but in a simple learner sentence like this, repeating een is the clearest and most standard choice.

So the best version is:

De radiator heeft een thermostaat en een radiatorknop.

It is a normal Dutch word: thermostaat.

It is related to the same international/technical word used in many languages, so it looks very familiar to English speakers. Even though it resembles English thermostat, in Dutch it is fully treated as a regular Dutch noun, with its own article:

• de thermostaat
• een thermostaat

In normal speech, een is often pronounced in a reduced way, more like uhn or 'n, especially when it is just the article a/an.

So in natural speech:

• een thermostaat
• een radiatorknop

may sound lighter and less stressed than in careful pronunciation.

Important distinction:

• een as the article a/an is often reduced
• één meaning one is stressed clearly

So in this sentence, it is just the unstressed article.

Yes, in this sentence en works just like English and.

It joins two nouns:

• een thermostaat
• een radiatorknop

So: een thermostaat en een radiatorknop = a thermostat and a radiator knob

Not always. They are related, but they do not mean exactly the same thing.

• radiator = the physical radiator unit
• verwarming = heating, or the heating system in general

So De radiator heeft ... refers to the object itself.
If you said De verwarming heeft ..., it might sound like you are talking about the heating system rather than one radiator, so the meaning changes.

The plural forms are:

• de radiator → de radiatoren
• de thermostaat → de thermostaten
• de radiatorknop → de radiatorknoppen

A useful thing to notice is that plural nouns in Dutch usually take de, even if the singular noun is a het-word. In this sentence, though, all the nouns shown are already de-words in the singular.