"He never reads."
Translation:Ní léann sé riamh.
ní is used to negative all verbs in the present and future tense.
In the case of the verb bí, the present tense dependent form, used after verbal particles, is fuil, so you get an bhfuil, go bhfuil etc, but what should be ní fhuil has become níl, because fh is silent.
So níl is only used if the positive version of the question would use tá. It has noting to do with vowels or consonants.
ní ithim cabáiste - "I don't eat cabbage"
ní léann sé an nuachtán - "he doesn't read the newspaper"
ní bhuailfidh tú leis - "you will not meet him"
níl sé fuar - "he is not cold"
tá sé fuair - "he is cold"
níl ocras orm - "I'm not hungry"
tá ocras orm - "I am hungry"
It is possible to use riamh with ní and with níl, because níl is just a special case of ní.