Sia che il bollitore funzioni, sia che si rompa, domattina berrò comunque il tè.

It means whether ... or ... / be it that ... or that ....

So:

• Sia che il bollitore funzioni, sia che si rompa
  = Whether the kettle works or breaks

This structure presents two possible situations, and the main clause stays true in either case.

A very natural English equivalent here is:

• Whether the kettle works or breaks, I’ll drink tea tomorrow morning anyway.

It is a fixed Italian pattern:

• sia che + subjunctive, sia che + subjunctive

You will often see it in sentences expressing it doesn’t matter which of two possibilities happens.

Yes. Sia is the present subjunctive form of essere for lui/lei and also Lei.

In the expression sia che ... sia che ..., the word sia comes from essere, but in this pattern it functions as part of a set expression rather than carrying its usual full meaning of is/be by itself.

So even though sia is technically a verb form of essere, in this construction you should mostly learn sia che ... sia che ... as a whole pattern meaning whether ... or ....

Because the structure sia che ... sia che ... normally requires the subjunctive.

Here you have:

• funzioni = present subjunctive of funzionare
• si rompa = present subjunctive of rompersi

This happens because the sentence is talking about possible alternatives, not stating simple facts.

Compare:

• Il bollitore funziona. = The kettle works.
  This is a straightforward statement, so the indicative is used.

But:

• Sia che il bollitore funzioni, sia che si rompa...
  = Whether the kettle works or breaks...
  This presents possibilities, so Italian uses the subjunctive.

Because the standard pattern is:

• sia che + clause, sia che + clause

So each alternative is introduced by its own che.

That is why you get:

• sia che il bollitore funzioni
• sia che si rompa

This repetition is normal and expected in Italian. It helps clearly mark the two parallel alternatives.

Si rompa comes from rompersi, which means to break or to get broken.

In this sentence:

• il bollitore si rompa
  means the kettle breaks / the kettle gets broken

The si is part of the verb rompersi, which is often used for things breaking on their own or ending up broken.

Compare:

• rompere qualcosa = to break something
  
  • Rompo il bicchiere. = I break the glass.
• rompersi = to break / to get broken
  
  • Il bicchiere si rompe. = The glass breaks.

So here, the kettle is not breaking something else; it is the thing that breaks.

Because bere has an irregular future stem.

The future of bere is:

• berrò
• berrai
• berrà
• berremo
• berrete
• berranno

So:

• domattina berrò comunque il tè
  = tomorrow morning I’ll drink tea anyway

This is one of those verb forms you just need to learn as irregular.

Comunque means anyway, in any case, or regardless.

It emphasizes that the result in the main clause does not depend on which alternative happens.

So the logic is:

• the kettle may work
• or it may break
• either way, I’ll still drink tea

That is exactly what comunque highlights.

You can often place comunque in different spots, for example:

• Domattina berrò comunque il tè.
• Domattina comunque berrò il tè.

The version in your sentence is very natural.

Yes, you can also say domani mattina.

Both are natural:

• domattina
• domani mattina

They both mean tomorrow morning.

Domattina is simply a common fused form. In everyday Italian, both versions are widely used.

So these are both fine:

• Domattina berrò il tè.
• Domani mattina berrò il tè.

Italian often uses the definite article with nouns in places where English would not.

So:

• berrò il tè = I’ll drink tea

The article does not necessarily mean a specific cup already identified in the conversation. It is often just the normal Italian way to talk about a drink, food, or a general item in context.

Without the article, berrò tè, it would sound unusual in most normal contexts.

Compare:

• Bevo il caffè. = I drink coffee.
• Mangio la pasta. = I eat pasta.

Italian commonly uses the article here where English does not.

Because the noun tè is spelled with a grave accent to distinguish it from te, the unstressed object pronoun meaning you.

So:

• tè = tea
• te = you

Examples:

• Bevo il tè. = I drink tea.
• Vedo te. = I see you.

The accent is important in writing.

In standard Italian, no. That would sound wrong because after sia che ... sia che ..., you normally need the subjunctive, not the indicative.

So the correct forms are:

• funzioni
• si rompa

Not:

• funziona
• si rompe

A good rule to remember is:

• sia che + subjunctive
• sia che + subjunctive

Yes. Italian often drops subject pronouns when the verb ending already makes the subject clear.

• berrò already means I will drink

So:

• Domattina berrò comunque il tè naturally means
• Tomorrow morning I will drink tea anyway

You could say io berrò, but that would usually add emphasis, for example:

• Io berrò comunque il tè.
  = I will drink tea anyway.

Without special emphasis, leaving out io is the normal choice.

It is perfectly correct and natural, but it is a little more structured and polished than the most casual everyday phrasing.

A speaker might also say something simpler in conversation, such as:

• Che il bollitore funzioni o si rompa, domattina berrò comunque il tè.
• Funzioni o si rompa, domattina berrò comunque il tè.
  This second one is more compressed and depends on context.

But your original sentence is absolutely normal and elegant. It is a good model for learning the sia che ... sia che ... construction.