Verificăm încălzitorul cu termometrul.

Verificăm is the 1st person plural present tense form of a verifica (to check / to verify).

So:

• eu verific = I check
• tu verifici = you check
• noi verificăm = we check

The ending -ăm tells you the subject is we.

Romanian often drops subject pronouns when they are not needed, because the verb ending already shows who is doing the action.

So:

• Verificăm already means we check
• Noi verificăm would also be correct, but noi is usually added only for emphasis or contrast

For example:

• Noi verificăm încălzitorul, nu ei. = We are checking the heater, not them.

The ending -ul is the Romanian definite article, attached to the end of a masculine/neuter singular noun.

So:

• încălzitor = heater
• încălzitorul = the heater

and:

• termometru = thermometer
• termometrul = the thermometer

Unlike English, Romanian usually puts the at the end of the noun rather than as a separate word before it.

The thing being checked is încălzitorul because it is the direct object of the verb.

The phrase cu termometrul means with the thermometer and shows the instrument used to do the checking.

So the structure is:

• Verificăm = we check
• încălzitorul = the heater
• cu termometrul = with the thermometer

That tells you the sentence means: We check the heater with the thermometer.

Here, cu means with, in the sense of using something as a tool or instrument.

So:

• cu termometrul = with the thermometer

In this sentence, it does not mean companionship like together with. It means by using the thermometer.

Not as a normal separate case ending in the way some other languages do. Romanian usually expresses the idea of an instrument with the preposition cu.

So English with a thermometer is normally Romanian cu un termometru, and with the thermometer is cu termometrul.

The job that an instrumental case would do in some languages is usually handled in Romanian by cu + noun.

Because after cu, Romanian normally keeps the noun in the regular form that fits the phrase, and the noun can still be definite.

So:

• cu un termometru = with a thermometer
• cu termometrul = with the thermometer

The preposition cu does not remove definiteness. You can still say the thermometer, just as in English.

It is made of:

• încălzitor = heater
• -ul = the

So:

• încălzitorul = the heater

The noun încălzitor is related to the verb a încălzi (to heat / to warm), so it is literally something like heater / warming device.

Yes. Romanian word order is somewhat flexible, although this sentence has a very natural neutral order.

Neutral order:

• Verificăm încălzitorul cu termometrul.

For emphasis, you could also say:

• Cu termometrul verificăm încălzitorul.
  = It’s with the thermometer that we check the heater.

But the original version is the most straightforward everyday wording.

Yes, but the meaning would become less specific.

Compare:

• Verificăm încălzitorul cu termometrul. = We check the heater with the thermometer.
• Verificăm un încălzitor cu un termometru. = We check a heater with a thermometer.

So the sentence you have points to specific, known items: a particular heater and a particular thermometer.

A simple English-friendly approximation is:

veh-ree-fee-KUHm uhn-kuhl-zee-TOH-rool koo ter-moh-MEH-trool

A few useful notes:

• ă is a short central vowel, something like the a in sofa
• î is a distinct Romanian vowel with no exact English equivalent
• stress is roughly on:
  • verificăm
  • încălzitorul
  • termometrul

They are:

• a verifica = to check / to verify
• încălzitor = heater
• cu = with
• termometru = thermometer

In the sentence, these appear as:

• verificăm = we check
• încălzitorul = the heater
• termometrul = the thermometer

A little, if you look only at the English translation, because English with the thermometer might sometimes feel loose. But in Romanian, the structure clearly points to:

• încălzitorul as the thing checked
• cu termometrul as the instrument used

If you changed the sentence to:

• Verificăm termometrul cu încălzitorul.

then the meaning would switch to:

• We check the thermometer with the heater

So Romanian relies strongly on the sentence structure and the prepositional phrase to show these relationships clearly.