Hverken termostaten eller radiatorventilen virker.

Hverken ... eller ... is the Danish equivalent of neither ... nor ....

In this sentence:

• hverken termostaten eller radiatorventilen = neither the thermostat nor the radiator valve

It connects two alternatives and says that both are excluded.

A useful pattern is:

• hverken + noun + eller + noun + verb

For example:

• Hverken kaffen eller teen er varm.
• Hverken Peter eller Anna kommer.

So in your sentence, the speaker is saying that both items fail to work.

In Danish, the definite article is usually attached to the end of the noun instead of being a separate word before it.

So:

• termostat = thermostat
• termostaten = the thermostat

and:

• radiatorventil = radiator valve
• radiatorventilen = the radiator valve

This is one of the big differences from English. English says the thermostat, but Danish usually says termostaten.

The ending -en is the common definite singular ending for many common-gender nouns in Danish.

Here:

• en termostat → termostaten
• en radiatorventil → radiatorventilen

So the -en here means the.

This does not mean the nouns are plural. They are singular definite.

Danish, like German, often forms compound nouns by writing them as one word.

So:

• radiator
  • ventil = radiatorventil
• radiatorventilen = the radiator valve

English often uses separate words where Danish prefers one compound word.

More examples:

• toothbrush type compounds in English are similar
• Danish does this even more often:
  • sommerhus
  • arbejdsdag
  • fjernbetjening

So radiatorventilen is completely normal Danish spelling.

Virker is the present tense of virke, which often means to work, to function, or sometimes to seem, depending on context.

In this sentence it means to function / to work.

So:

• Termostaten virker. = The thermostat works.
• Det virker mærkeligt. = It seems strange.

That means virke is a very common Danish verb with more than one possible English translation, and context tells you which meaning is intended.

Because hverken ... eller ... already contains the negative idea.

English works the same way:

• Neither the thermostat nor the radiator valve works.

You do not normally say:

• Neither the thermostat nor the radiator valve doesn’t work.

That would be a double negative in standard English, and the same basic logic applies in Danish.

So:

• Hverken ... eller ... already does the job of negation
• no extra ikke is needed

This is a very common question for English speakers.

The short answer is: Danish verbs do not change form for person or number in the present tense the way English verbs sometimes do.

So:

• jeg virker
• du virker
• den virker
• vi virker
• de virker

The form stays virker.

That means it is not useful to think of virker here as specifically singular or plural. It is simply the present-tense form.

Compare with English:

• it works
• they work

English changes the verb form a little. Danish does not.

Yes. The whole phrase hverken termostaten eller radiatorventilen functions as the subject.

Then the verb is:

• virker

So the sentence structure is:

• Subject: Hverken termostaten eller radiatorventilen
• Verb: virker

This is useful because learners sometimes wrongly think hverken stands outside the grammar of the sentence. It does not. It is part of the subject phrase here.

Yes. That is the positive opposite.

• Hverken termostaten eller radiatorventilen virker. = neither one works
• Både termostaten og radiatorventilen virker. = both work

This is a very helpful pair to learn together:

• hverken ... eller ... = neither ... nor ...
• både ... og ... = both ... and ...

Hverken can look intimidating because Danish spelling and pronunciation do not always match in an obvious way for English speakers.

A rough guide is that it sounds something like:

• VER-ken or VAIR-ken, depending on accent and how precise you want to be

A few notes:

• the hv combination in modern Danish is usually pronounced with just a v sound
• the r affects the vowel quality
• the final -en is usually fairly light

You do not need to pronounce every written letter very strongly. That is normal in Danish.

Often, yes.

• virker = works / functions
• fungerer = functions / works

In many practical situations, both are possible:

• Termostaten virker ikke.
• Termostaten fungerer ikke.

However, virke is often more common and more flexible in everyday Danish. It can also mean seem, which fungere usually cannot.

So in your sentence, virker is very natural.

Yes. Danish is a verb-second language in main clauses.

Your original sentence starts with the subject:

• Hverken termostaten eller radiatorventilen virker.

If you move another element to the front, the finite verb normally comes second:

• I dag virker hverken termostaten eller radiatorventilen.

Notice what happened:

• I dag comes first
• virker comes second
• the subject comes after the verb

This is a very important Danish word-order rule, and it applies broadly, not just with hverken ... eller ....