Ako se mikrovalna opet pokvari, grijat ćemo juhu na štednjaku dok majstor ne popravi bojler.

Because Croatian often uses an adjective as a noun when the full noun is obvious from context.

• Full expression: mikrovalna pećnica = microwave oven
• Shortened everyday form: mikrovalna = microwave

This is why the word is feminine: it comes from the omitted noun pećnica, which is feminine.

Here se is part of the verb expression pokvariti se, which means to break down / to stop working.

Compare:

• pokvariti nešto = to spoil / break something
• pokvariti se = to go wrong / break down

So:

• Mikrovalna se pokvarila. = The microwave broke down.

The se here is not really translated as itself in English; it is just how this verb works in Croatian.

After ako (if), Croatian normally uses the present tense, not the future tense.

So Croatian says:

• Ako se mikrovalna opet pokvari...

even though English says:

• If the microwave breaks down again...

In addition, pokvari is a perfective present form, so it refers to a single completed event in the future: if it breaks down.

This is very normal in Croatian:

• Ako dođe, javit ću ti. = If he comes, I’ll let you know.

This is the standard way of writing the future when the auxiliary comes after the infinitive.

The verb is grijati = to heat.
Future auxiliary: ćemo = we will

When ćemo comes after the infinitive, the final -i of the infinitive is dropped in writing:

• grijati
  • ćemo → grijat ćemo

Compare:

• Ćemo grijati juhu. = full infinitive after the auxiliary
• Grijat ćemo juhu. = shortened infinitive before the auxiliary

Both mean the same thing, but grijati ćemo is not the standard spelling.

Because juhu is the accusative singular, and here soup is the direct object of grijat ćemo.

Base form:

• juha = soup

Direct object form:

• juhu = soup (as the thing being heated)

This is a very common pattern for feminine nouns ending in -a:

• kava → kavu
• voda → vodu
• juha → juhu

Because na here means on, and it is followed by the locative case to show location.

• štednjak = stove
• na štednjaku = on the stove

So:

• grijat ćemo juhu na štednjaku = we’ll heat the soup on the stove

A useful contrast:

• na štednjaku = on the stove (location, locative)
• na štednjak = onto the stove (movement toward it, accusative)

Here it means until.

Croatian dok can mean either while or until, depending on the structure.

In this sentence:

• dok majstor ne popravi bojler

it means until the repairman fixes the boiler/water heater.

If it meant while, the structure would usually look different, often with an imperfective verb and without this dok ... ne + perfective pattern.

Because in this pattern, ne does not make the clause negative in the normal sense.

With dok meaning until, Croatian very often uses:

• dok + subject + ne + perfective verb

So:

• dok majstor ne popravi bojler = until the repairman fixes the boiler

The repair is expected to happen. This ne is just part of the standard grammar of this construction.

This is a common thing for English speakers to notice, because it looks like not fixes, but that is not how it functions here.

Because popravi is perfective, and the sentence is talking about the moment the repair is completed.

• popraviti = to fix, to finish fixing (perfective)
• popravljati / popravljati = to be fixing / to fix repeatedly (imperfective)

With dok ... ne, Croatian usually wants the endpoint:

• dok majstor ne popravi bojler = until the repairman fixes the boiler

If you used an imperfective form, it would suggest an ongoing process rather than completion, which would not fit as well here.

Because Croatian has no articles like a or the.

So:

• majstor can mean a repairman or the repairman
• bojler can mean a boiler/water heater or the boiler/water heater

The exact meaning comes from context. In this sentence, English naturally uses the repairman and the boiler/water heater, but Croatian does not need separate article words.

Yes. Croatian word order is more flexible than English word order.

For example, you could also say:

• Ako se mikrovalna opet pokvari, juhu ćemo grijat na štednjaku dok majstor ne popravi bojler.

That still means the same thing.

However, the original sentence sounds natural because:

• ćemo is a clitic, so it tends to appear near the beginning of its clause
• grijat ćemo is a very common future pattern
• opet is placed naturally before pokvari

So the word order is flexible, but not random. Some positions sound more natural than others.

Not always.

In everyday Croatian, bojler often means a water heater, especially the kind used for hot water in a home. In English, boiler can sometimes suggest a larger heating system, depending on the variety of English.

So in many contexts, water heater is the safest translation of bojler.