Tôi muốn yêu cầu hoàn tiền khi còn bảo hành.

A word-by-word breakdown is:

• Tôi = I
• muốn = want
• yêu cầu = request / ask for
• hoàn tiền = refund / return the money
• khi = when
• còn = still / remaining
• bảo hành = warranty / under warranty

So the structure is roughly:

• Tôi muốn = I want
• yêu cầu hoàn tiền = to request a refund
• khi còn bảo hành = while it is still under warranty

Vietnamese often leaves out words that English would include if the meaning is clear from context.

Yes, you often can drop tôi in conversation if the subject is obvious.

• Tôi muốn yêu cầu hoàn tiền... = more explicit, neutral, complete
• Muốn yêu cầu hoàn tiền... = less complete, but possible in context

However, for learners, keeping tôi is safer because:

• it makes the sentence clear
• it sounds complete
• it avoids ambiguity

So tôi is a good default choice.

Yes, literally it is close to I want to request.

Vietnamese often puts verbs together without needing a separate word for to:

• muốn ăn = want to eat
• muốn hỏi = want to ask
• muốn yêu cầu = want to request

So muốn + verb works like want to + verb in English.

Yêu cầu can mean request, ask for, or sometimes demand, depending on context.

In everyday use:

• yêu cầu hoàn tiền = request a refund
• yêu cầu hỗ trợ = request support
• yêu cầu bồi thường = request compensation

It can sound a little formal or firm. If you want something softer in customer-service situations, people may also say:

• xin hoàn tiền = ask for a refund
• muốn được hoàn tiền = want to be refunded

So yêu cầu is not wrong, but it can sound more official than casual speech.

Yes, hoàn tiền is a very common fixed expression meaning refund or return money.

Examples:

• chính sách hoàn tiền = refund policy
• yêu cầu hoàn tiền = request a refund
• được hoàn tiền = be refunded

A related expression is:

• trả lại tiền = return the money

Both can work, but hoàn tiền is especially common in formal, business, and customer-service language.

Literally, it means something like:

• khi = when
• còn = still
• bảo hành = under warranty / warranty

So the idea is when it is still under warranty.

The word còn is important here. It gives the sense of still or not expired yet.

Compare:

• còn bảo hành = still under warranty
• hết bảo hành = out of warranty / warranty has expired

So khi còn bảo hành means the warranty period is still valid.

Because Vietnamese often omits things that are understood from context.

In English, you would usually say:

• when it is still under warranty
• while the product is still under warranty

In Vietnamese, if everyone already knows you are talking about a product, you can simply say:

• khi còn bảo hành

The product is implied.

If you want to be more explicit, you could say:

• khi sản phẩm còn bảo hành
• khi sản phẩm vẫn còn trong thời gian bảo hành

These are fuller versions.

It is behaving more like a warranty-related state or condition here.

Bảo hành can be used in different ways:

• as a noun-like idea: warranty
• as part of a verbal expression: bảo hành sản phẩm = warranty the product
• in the phrase còn bảo hành = still under warranty

So in khi còn bảo hành, you should understand it as while still under warranty, not as a direct action.

It is understandable, but it is slightly stiff and not the most natural version in many real-life situations.

More natural alternatives might be:

• Tôi muốn yêu cầu được hoàn tiền khi sản phẩm còn bảo hành.
• Tôi muốn xin hoàn tiền khi sản phẩm هنوز còn bảo hành. -> Wait, that includes a non-Vietnamese word? No, avoid this.
• Tôi muốn xin hoàn tiền khi sản phẩm còn bảo hành.
• Tôi muốn được hoàn tiền khi sản phẩm vẫn còn trong thời gian bảo hành.

Why the original can feel a bit stiff:

• yêu cầu sounds formal/official
• khi còn bảo hành is a little shortened
• adding sản phẩm makes the meaning clearer

So the original is valid, but a slightly smoother version would be:

• Tôi muốn yêu cầu hoàn tiền khi sản phẩm còn bảo hành.

or more naturally in customer-service speech:

• Tôi muốn xin hoàn tiền khi sản phẩm còn bảo hành.

Vietnamese usually does not mark tense the way English does.

Tôi muốn yêu cầu hoàn tiền khi còn bảo hành does not specifically mark past, present, or future. The time is understood from:

• context
• surrounding sentences
• time words, if any

Here, muốn already tells you this is about a present intention or desire:

• Tôi muốn... = I want...

If you needed a clearer time reference, you could add words like:

• bây giờ = now
• hiện tại = currently
• sắp tới = soon
• đã = past marker
• sẽ = future marker

But in this sentence, extra tense marking is not necessary.

Often, yes.

Both are understandable, but they feel a little different:

• khi còn bảo hành = when still under warranty
• trong thời gian bảo hành = during the warranty period

Trong thời gian bảo hành is more explicit and often sounds smoother in formal or customer-service contexts.

For example:

• Tôi muốn yêu cầu hoàn tiền trong thời gian bảo hành.

That said, khi còn bảo hành is shorter and still natural enough, especially in speech.

You can make it softer by replacing the more forceful/formal yêu cầu with gentler wording.

Some options:

• Tôi muốn xin hoàn tiền khi sản phẩm còn bảo hành.
• Tôi muốn được hoàn tiền khi sản phẩm còn bảo hành.
• Tôi muốn hỏi về việc hoàn tiền khi sản phẩm còn bảo hành.

These feel less like a formal demand and more like polite customer communication.

A useful distinction:

• yêu cầu hoàn tiền = request/demand a refund
• xin hoàn tiền = ask for a refund
• muốn được hoàn tiền = want to be refunded

If you are speaking to customer service, xin hoàn tiền is often a good choice.

A natural grouping would be:

• Tôi muốn / yêu cầu hoàn tiền / khi còn bảo hành.

The main meaning units are:

1. Tôi muốn
2. yêu cầu hoàn tiền
3. khi còn bảo hành

You would usually give a little emphasis to:

• muốn
• hoàn tiền
• bảo hành

Very roughly, the flow is:

• Tôi muốn
• yêu cầu hoàn tiền
• khi còn bảo hành

If you are practicing, say it slowly in chunks first, then more smoothly.