التدفئة المركزية تعمل اليوم.

A careful MSA pronunciation is:

at-tadfiʾatu al-markaziyyatu taʿmalu al-yawma

In normal everyday reading without case endings, many learners say it more like:

at-tadfiʾa al-markaziyya taʿmal al-yawm

A few pronunciation notes:

• التدفئة starts with at-, not al-, because of assimilation.
• تعمل contains ع (ʿayn), a throat sound with no exact English equivalent.
• اليوم is pronounced al-yawm.

Because ت is a sun letter.

In Arabic, when الـ comes before a sun letter, the ل sound assimilates to the next consonant. So:

• التدفئة is pronounced at-tadfiʾa, not al-tadfiʾa

But in المركزية, the first letter after الـ is م, which is a moon letter, so the ل is pronounced normally:

• المركزية = al-markaziyya

This is a very common feature of Arabic pronunciation.

التدفئة is a noun meaning heating.

More specifically, it is a verbal noun or maṣdar, related to the verb دفّأ meaning to heat or to warm.

So التدفئة is not a verb here. It is the noun heating, as in:

• central heating
• home heating
• heating system

It is also treated as a feminine singular noun.

Because المركزية is an adjective meaning central, and in Arabic:

1. Adjectives usually come after the noun
2. They must agree with the noun in:
   • definiteness
   • gender
   • number
   • and, in fully vowelled Arabic, case

So:

• التدفئة = the heating
• المركزية = the central

Together: التدفئة المركزية = the central heating

Since the noun is definite with الـ, the adjective must also be definite with الـ.

Because it agrees with التدفئة, which is feminine singular.

The basic adjective is:

• مركزي = central (masculine)
• مركزية = central (feminine)

Since التدفئة is feminine, Arabic uses the feminine form:

• التدفئة المركزية

This kind of adjective agreement is extremely important in Arabic.

Because the subject التدفئة المركزية is grammatically feminine singular.

The verb عمل can mean to work, to function, or to operate, depending on context. In the present tense:

• يعمل = he works / it works for a masculine singular subject
• تعمل = she works / it works for a feminine singular subject

Since التدفئة is feminine, Arabic uses:

• تعمل

Even though heating is not biologically female, grammatical gender still controls the verb form.

It can mean either, depending on context.

Arabic present-tense verbs often cover both:

• simple present: works
• present progressive: is working

So تعمل اليوم could be understood as:

• works today
• is working today

In natural English, is working today is often the best translation here, because it sounds like a current situation or status.

Because Arabic does not use the present-tense verb to be the same way English does.

In English, we say:

• is working

In Arabic, the single verb تعمل already carries that meaning:

• works
• is working

So Arabic does not need an extra word equivalent to English is here.

اليوم means today, and here it functions as an adverb of time.

Literally, it is related to the noun day, but in Arabic اليوم is the normal word for today.

Its الـ is just part of the standard word form. You do not remove it when you mean today.

So:

• اليوم = today

In fully vowelled formal Arabic, it is often analyzed as an accusative adverbial expression:

• اليومَ

But in normal writing, the final vowel is usually not written.

Yes. That is also correct.

Both of these are possible:

• التدفئة المركزية تعمل اليوم
• تعمل التدفئة المركزية اليوم

The difference is mainly one of style or emphasis:

• التدفئة المركزية تعمل اليوم starts with the topic the central heating, so it can feel slightly like As for the central heating, it’s working today.
• تعمل التدفئة المركزية اليوم is a more straightforward verb-first sentence.

Arabic word order is more flexible than English, though the choice can affect emphasis.

In fully vowelled formal MSA, it would be:

التدفئةُ المركزيةُ تعملُ اليومَ

These endings show the grammatical roles:

• التدفئةُ — nominative
• المركزيةُ — nominative adjective agreeing with التدفئة
• تعملُ — present-tense verb
• اليومَ — accusative adverb of time

In most modern writing, these final short vowels are omitted, so learners usually see:

التدفئة المركزية تعمل اليوم

Both refer to the same sentence; the second is just the normal unvowelled spelling.