The most common and most likely answer to this crossword clue is the 9 letter word RHEOSTATS
I've seen this crossword clue in The Daily Telegraph
R
H
E
O
S
T
A
T
S
Buddy explains!
The straight part
We know that "They control ovens" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they control ovens = rheostats.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RHEOSTATS mean?
RHEOSTATS noun- An electrical resistor, with two terminals, whose resistance is continuously variable by moving a knob or slider.