Had a blow-out, account unpaid (8)
I believe the answer is:
billowed
'had a blow-out' is the definition.
(to billow is to blow out or swell with air)
'account unpaid' is the wordplay.
'account' becomes 'bill' (synonyms).
'unpaid' becomes 'owed' (similar in meaning).
'bill'+'owed'='BILLOWED'
(Other definitions for billowed that I've seen before include "Swollen account was due payment" , "was swelling" , "Flowed with an undulating motion; filled with air" .)