Problem caused by a cold potato dish -- colcannon, primarily (8)
I believe the answer is:
acrostic
'problem' is the definition.
(acrostic is a kind of problem)
'a cold potato dish colcannon primarily' is the wordplay.
'cold' becomes 'C' (eg on taps).
'potato dish' becomes 'rosti' (I've seen this before).
'primarily' suggests taking the first letters.
The initial letter of 'colcannon' is 'c'.
'a'+'c'+'rosti'+'c'='ACROSTIC'
'caused by' acts as a link.
(Other definitions for acrostic that I've seen before include "Socratic kind of old word puzzle" , "Legal document" , "RAC stoic (anag) - lines of writing where certain initial letters form a word or proverb" , "Poem with word(s) reading downwards" , "Puzzle involving leading characters" .)