Chimney suction still weak after cleaning? Here is what got missed

Clean filters are a good start, but they are the easy part. If suction did not come back, the restriction is somewhere the sponge did not go.

The fan blades

Behind the filters, the impeller collects the same oil the filters missed. A few millimetres of grease on each blade changes the shape enough to halve the airflow. It needs the housing opened to clean properly.

The housing walls

Around the fan, the inside of the chimney body builds a coating too. On older units it is thick enough to scrape.

The duct

Especially the first bend above the chimney, where warm greasy air first slows down. A flexible aluminium duct with a few years on it can be a third blocked and look fine from below.

The outlet

Flap glued shut, cowl nested in, or a mesh someone fitted against insects that is now solid with grease.

If the chimney is also noisier than it was, the motor is probably straining against one of these, and the sooner it is relieved the longer it lasts.

What a full service does differently

It opens the housing. That is the whole difference. Filters are twenty minutes; the fan, housing and reachable duct are the rest of the hour, and they are where the suction went.