Affecting: Peugeot 308 all models
This fault is usually noticed as not getting any hot air into the cabin, no matter how warm the engine is.
The problem is caused by a blocked heater matrix. The only proper cure we've found is to replace the heater matrix. Its a fairly straightforward job. The cause is limescale or similar contamination blocking the coolant flow through the matrix. In extreme cases we've found the engine radiator partially blocked necessitating replacement, so it's important to drain / flush the system to prevent the new matrix getting blocked. It also calls into question the coolant replacement interval, as there is no recommendation by the manufacturer to replace the coolant in the service schedule.