Complex first stage for heating engineers? (3,7)

I believe the answer is:

gas-fitters

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'heating engineers?' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'complex first stage' is the wordplay.
'complex' indicates an anagram.
'first'+'stage'='firststage'
'firststage' is an anagram of 'GAS-FITTERS'.

'for' acts as a link.

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I've seen this clue in The Guardian.

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