Very first thing to do is check the oil. Both the condition and the level. If either are not acceptable, this this could be your issue. A change of fluid and filter including a full flush has been known to fix this issue. It could be a sticking solenoid which would need cleaning or replacing also. How many miles on it and has it a full service history?
OK. Make it perfectly clear that you want the system flushed. And it is crucial that they use the exact specified oil that Peugeot recommend. Do not allow them to put anything else in. Do not compromise.
Dealerships tend to provide sh$thouse service with a zero care factor. You are better off finding a Pug specialist mechanic to look after it.
What model is it Cass?