Boiled pudding is no good (4)
I believe the answer is:
duff
This clue is a double definition.
'boiled pudding' is the first definition.
(I've seen this before)
'no good' is the second definition.
(I've seen this before)
'is' acts as a link.
(Other definitions for duff that I've seen before include "Worthless; pudding" , "Pudding - of poor quality - Homer Simpson's favourite beer" , "Pudding -- useless -- Homer Simpson's kind of beer" , "Dud - pud" , "Heavy pudding - no good" .)