Si el somier vuelve a estar suelto esta noche, mi padre revisará otra vez la tuerca y el cabecero.

This is the normal pattern for a real or likely future condition in Spanish:

• Si + present indicative, + future
• Si vuelve a estar suelto, revisará...

English often does something similar:

• If it is loose tonight, my father will check...

Spanish does not normally use the future directly after si in this kind of sentence, so si volverá would be wrong here.

Volver a + infinitive is a very common Spanish structure meaning to do something again.

So:

• vuelve a estar suelto = becomes/is loose again
• literally, returns to being loose

You could also say:

• Si el somier está otra vez suelto...

That is also understandable, but vuelve a estar suelto sounds very natural because it focuses on the idea that the same problem happens again.

It means to do something again.

Examples:

• volver a intentar = try again
• volver a llamar = call again
• volver a estar suelto = be loose again

In this sentence, volver a estar is not about physically returning somewhere. It is a fixed verbal structure meaning to be in that state again.

In Spain, somier usually means the bed base or slatted frame that supports the mattress.

It is not the mattress itself. Depending on context, it may refer to:

• a slatted base
• a metal bed base
• the support structure under the mattress

This is a very Spain-specific household word, so it is useful to learn it as furniture vocabulary.

Here suelto means loose, not firmly attached, or coming undone.

For example:

• un tornillo suelto = a loose screw
• una rueda suelta = a loose wheel

In this sentence, it suggests the bed base is not properly fixed.

Be careful: suelto can have other meanings in other contexts, such as single/individual or let loose, but here it clearly means loose in a mechanical sense.

Sometimes, but the nuance is a bit different.

• suelto usually means detached, loose, not properly fixed
• flojo often means slack, weak, not tight enough

For a bed part, suelto is very natural if something is coming loose.
If you wanted to emphasize that something is not tightened enough, flojo could also appear in some contexts.

So suelto is a good choice here because it sounds like a fitting or fastening problem.

Esta noche is the normal and standard way to say tonight in Spanish.

• esta noche = tonight

Hoy por la noche also exists and means tonight / this evening, but it is a little longer.

Hoy noche is not the usual standard expression in modern Spanish.

This is a useful false-friend question.

In many contexts, revisar means:

• to check
• to inspect
• to look over

So here:

• mi padre revisará la tuerca y el cabecero = my father will check/inspect the nut and the headboard

It does not mean revise in the English schoolwork sense here.

Spanish revisar can sometimes overlap with English review, check, or inspect, depending on context.

Otra vez means again.

So:

• revisará otra vez = he will check again

You can often replace it with de nuevo:

• revisará de nuevo

Both are correct.
Very generally:

• otra vez is very common in everyday speech
• de nuevo can sound slightly more formal or neutral in some contexts

In this sentence, otra vez sounds perfectly natural.

Spanish uses definite articles more often than English.

Here the articles point to specific things that both speaker and listener can identify:

• the bed base
• the nut
• the headboard

Even if English might sometimes omit an article in a practical household context, Spanish usually keeps it:

• revisará la tuerca y el cabecero

This sounds natural because it refers to the particular parts of that bed.

Cabecero means headboard.

It is the part at the head of the bed. In Spain, cabecero is the normal word for this item of furniture.

So in the sentence, the father is going to check:

• la tuerca = the nut
• el cabecero = the headboard

This suggests the looseness may be caused by how the bed frame is connected.

No. Tuerca means nut.

Compare:

• tornillo = screw/bolt
• tuerca = nut

A tuerca is the piece that screws onto a bolt or threaded rod. So if a bed is loose, checking la tuerca makes a lot of sense.

Because this is a normal open condition about a possible real situation.

After si, Spanish usually uses the indicative for real or likely conditions:

• Si está...
• Si vuelve...

The subjunctive does not normally appear directly after si in this kind of sentence.

Common pattern:

• Si + present indicative, future
• Si + imperfect subjunctive, conditional

For example:

• Si vuelve a estar suelto, mi padre revisará...
• Si volviera a estar suelto, mi padre revisaría...

The second one sounds more hypothetical or less likely.

Yes, depending on how you interpret vuelve a estar suelto.

Because the phrase focuses on the state estar suelto, the most literal meaning is:

• is loose again

But in natural English, you might also say:

• gets loose again

That can sound more natural if you want to emphasize the change into that loose state. Spanish itself is describing the state, not necessarily the moment of change, but both English renderings can fit the context.

Yes, it is completely natural.

Spanish often uses:

• condition first
• main result second

So:

• Si el somier vuelve a estar suelto esta noche, mi padre revisará...

This is the same basic logic as English:

• If the bed base is loose again tonight, my father will check...

You could sometimes move things around for emphasis, but the given order is standard and clear.