Voisitteko tarkistaa, onko venttiili rikki?

Voisitteko is the conditional form of voida (to be able to / can) plus the question marker -ko.

• voitteko = can you?
• voisitteko = could you?

In requests, the conditional makes the sentence softer and more polite, much like English could you instead of can you.

So:

• Voitteko tarkistaa...? = Can you check...?
• Voisitteko tarkistaa...? = Could you check...?

The version in your sentence is more polite and natural in many service or formal situations.

-ko / -kö is the Finnish yes/no question marker.

It turns a statement into a question.

Examples:

• voisitte = you could
• voisitteko = could you?

and

• on = is
• onko = is ...?

So in this sentence, Finnish uses the question marker twice because there are two question-like parts:

1. Voisitteko tarkistaa... = the main polite request
2. onko venttiili rikki = the embedded yes/no question, whether the valve is broken

Because it follows voida.

In Finnish, after modal verbs like voida (can / could), the main action is usually in the first infinitive form.

So:

• voisitteko tarkistaa = could you check
• literally: could-you check

This is similar to English:

• could you check
• not could you checks

Other examples:

• Voinko tulla? = Can I come?
• Voisitko auttaa? = Could you help?

In all of these, the second verb stays in the infinitive.

It can be either:

1. plural you — when speaking to more than one person
2. polite singular you — when addressing one person formally or politely

This is because Finnish uses the 2nd person plural form as a polite form of address, somewhat like old-fashioned English you vs thou, or like polite plural forms in many European languages.

So Voisitteko tarkistaa...? may mean:

• Could you all check...?
• Could you check...? said politely to one person

In real life, context tells you which one is meant.

Because onko venttiili rikki is a subordinate clause.

The main clause is:

• Voisitteko tarkistaa = Could you check

The subordinate clause is:

• onko venttiili rikki = whether the valve is broken

Finnish normally uses a comma before subordinate clauses like this.

So the comma marks the boundary between:

• the request to check
• and the thing being checked

It is an embedded yes/no question, often translated with whether or if in English.

Compare:

• Onko venttiili rikki? = Is the valve broken?
  This is a direct question.

• Voisitteko tarkistaa, onko venttiili rikki? = Could you check whether the valve is broken?
  This is an embedded question inside a larger sentence.

Finnish uses the same -ko question marker in the embedded clause, so the question structure stays visible.

Because Finnish yes/no questions typically put the finite verb first, with -ko/-kö attached.

So:

• Venttiili on rikki. = The valve is broken.
• Onko venttiili rikki? = Is the valve broken?

That same question order remains inside the embedded clause:

• ..., onko venttiili rikki = ..., whether the valve is broken

So the structure is normal Finnish question word order, even though it is inside a larger sentence.

Rikki means broken here, but grammatically it behaves a bit differently from many ordinary adjectives.

In sentences like:

• Venttiili on rikki. = The valve is broken.

rikki works as a predicate complement describing the state of the valve.

A useful thing to notice is that rikki usually does not change form for number in this use:

• Venttiili on rikki. = The valve is broken.
• Venttiilit ovat rikki. = The valves are broken.

So unlike many adjectives, it stays rikki.

Because it is the subject of the clause onko venttiili rikki.

The basic dictionary form here is the nominative singular:

• venttiili = valve

In the clause:

• onko venttiili rikki

the valve is the thing being described as broken or not broken, so nominative is the normal form.

Not with the same meaning.

• Voisitteko tarkistaa, onko venttiili rikki?
  = Could you check whether the valve is broken?

This means the speaker does not know if it is broken.

But:

• Voisitteko tarkistaa, että venttiili on rikki?

sounds like Could you check that the valve is broken, which suggests the speaker is treating the valve being broken as the content to verify in a different way, and it is not the normal way to express whether or not.

So for whether/if in this kind of indirect yes/no question, Finnish uses onko, not että.

Yes. There are several possibilities depending on tone.

Less formal / less polite:

• Voitko tarkistaa, onko venttiili rikki?
  = Can/Could you check whether the valve is broken?
  This is for one person informally.

More direct:

• Tarkista, onko venttiili rikki.
  = Check whether the valve is broken.
  This is an imperative, so it sounds more like an instruction.

Another polite option:

• Tarkistaisitteko, onko venttiili rikki?
  = Would you check whether the valve is broken?

So the original sentence is polite, natural, and fairly formal.

Because Finnish often expresses whether/if in embedded yes/no questions by using a normal question form with -ko/-kö.

So instead of a separate word like English whether, Finnish says:

• onko venttiili rikki
• literally something like is-the-valve-broken?
• functionally: whether the valve is broken

This is very common in Finnish. English needs whether or if, but Finnish often just builds the embedded clause as a question.

A rough word-by-word breakdown is:

• Voisitteko = could you
• tarkistaa = check
• onko = is / whether ... is
• venttiili = the valve / valve
• rikki = broken

So the structure is roughly:

• Could you check, is the valve broken?

But natural English turns that into:

• Could you check whether the valve is broken?

So the Finnish sentence is quite compact, but its grammar is very systematic.