Trouble in service supplying gas (5)
I believe the answer is:
radon
'gas' is the definition.
(thesaurus)
'trouble in service' is the wordplay.
'trouble' becomes 'ado' (I've seen this before).
'in' means one lot of letters goes inside another.
'service' becomes 'rn' (abbreviation for Royal Navy).
'ado' put into 'rn' is 'RADON'.
'supplying' is the link.
(Other definitions for radon that I've seen before include "Radioactive gas, linked to granite" , "Rare noble gas" , "Noble gas, Rn" , "Gaseous element, Rn" , "A radioactive gas, symbol Rn" .)