Learn Hardcore Russian: Этот выключатель иногда не работает, поэтому стоит заменить его в выходные. - This switch sometimes doesn’t work, so it’s worth replacing it on the weekend.

Этот is the masculine singular nominative form of этот (this), and выключатель (switch) is masculine, so they agree: этот → этот выключатель.
Это выключатель is also possible, but it’s a different construction: это acts like this/it is in an identifying sentence (This is a switch / It’s a switch), not like an adjective modifying a noun.

What part of speech is выключатель, and how is it formed?

Выключатель is a masculine noun meaning (light) switch. It’s derived from the verb выключать / выключить (to switch off/turn off) with a common agent/instrument noun ending -тель, roughly a thing that switches off.

Why do we say иногда не работает and not just не работает иногда?

Both can be correct, but иногда не работает is a neutral, common word order: adverb (иногда) + negation + verb.
Не работает иногда is possible too, but it can sound more contrastive/emphatic (as if you’re focusing on sometimes as the key point).

What does не работает literally mean here? Is it “doesn’t work” or “isn’t working”?

Не работает is present tense imperfective, and Russian doesn’t strictly separate doesn’t work vs isn’t working the way English does. Context decides: here it means it fails to work sometimes / is unreliable.

Why is работает imperfective? Is there a perfective form?

Работать is the imperfective verb for to work / to function. It’s used for general states and repeated situations—perfect for иногда (sometimes).
There is a perfective form поработать but it means to work for a while, not to function (successfully), so it wouldn’t fit here.

What’s the function of поэтому and why is there a comma before it?

Поэтому means therefore / so / that’s why and introduces a result/consequence clause.
A comma is typically used because you’re joining two clauses:
1) Этот выключатель иногда не работает,
2) поэтому стоит заменить его в выходные.
Russian punctuation often marks this cause→result relationship with a comma.

What does стоит mean here? Is it the same as стоить (“to cost”)?

Here стоит is from стоить in the sense it’s worth (doing) / it would be a good idea (to do), not to cost money.
Common pattern: Стоит + infinitive = It’s worth / One should / It would be advisable to...
So стоит заменить = it’s worth replacing / we should replace.

Why is заменить perfective, and what would заменять change?

Заменить is perfective: it refers to a single completed action—replace it (once, successfully).
Заменять is imperfective and would imply an ongoing/repeated process or a general habit (to be replacing / to replace in general). In this context, a one-time replacement is intended, so заменить is natural.

Why is it заменить его—what case is его?

Его is the accusative (direct object) form of он (he/it) for masculine/neuter. It refers back to выключатель.
So: заменить (кого? что?) его = replace it.

Could we say заменить его на выходных instead of в выходные? What’s the difference?

Yes, both are common but slightly different in feel:

в выходные (accusative plural) often means during the weekend / on the weekend (as a time period), especially implying this coming weekend from context.
на выходных (prepositional plural with на) is very colloquial and means over the weekend / during the weekend.
Both work here; в выходные is a bit more neutral.

Why is выходные plural, and what exactly does it mean?

Выходные is plural because it literally means days off (usually Saturday + Sunday).
в выходные = on the weekend / during the weekend.
You can also hear выходной as a singular adjective meaning a day off (e.g., У меня завтра выходной = I have tomorrow off).

Does this sentence imply “this weekend” or “on weekends (in general)”?

By itself, в выходные can be interpreted as on the weekend (the upcoming one) in many everyday contexts, especially with a concrete task like replacing a switch.
If you want to force every weekend / generally, you’d more likely add something like по выходным (on weekends) or use a different context.

Could the subject be omitted in the second clause? Why doesn’t Russian repeat it?

Yes—Russian often avoids repeating the subject when it’s understood. After поэтому, the sentence naturally continues with an impersonal-style recommendation: стоит заменить... (literally it’s worth replacing...). No explicit subject like мы (we) is needed, and it sounds more natural without it.