Drop the metal grease filters and soak them flat in hot water with a non-caustic degreaser. If the hood recirculates rather than ducting outside, it also has a charcoal filter, which is replaced every six to twelve months and never washed. Then reach the impeller behind the filters.
Bosch hoods are competent, unglamorous and extremely common, which means most of them are installed and then ignored until something smells. The general method for any hood, filters out, soaked flat, then the impeller housing behind them, is covered on our rangehood cleaning guide. What follows is what is particular to a Bosch.
It is a BSH hood, and that is genuinely useful
Bosch, Neff and Siemens are all BSH brands, and their rangehoods share a great deal of engineering: filter dimensions, motor assemblies and mounting arrangements are frequently common across the three.
That matters in one practical situation. Hood filters lose their labels, model stickers fade in a warm greasy environment, and replacement filters are often listed by dimension rather than by badge. If you cannot find a Bosch part for an older hood, the equivalent Neff or Siemens listing is worth checking, because there is a reasonable chance it is the same component in a different box.
It also means that if you have a mixed BSH kitchen, which is common where appliances were bought at different times, the same approach applies to all of them.
Ducted or recirculating decides half the job
Ducted hoods push air outside. They carry metal grease filters only.
Recirculating hoods filter the air and return it to the kitchen. They have the same metal filters plus a charcoal filter behind them to take out the odour.
Charcoal filters are a consumable. They are not washable, they never have been, and washing one produces a wet obstruction that restricts airflow while doing nothing for smell. Replace them every six to twelve months depending on how hard the kitchen works.
This is worth checking on a Bosch specifically, because a lot of them are installed in apartments where ducting outside was never an option, and a great many of those have a charcoal filter that has been in place since the building was finished.
The filters themselves
Most Bosch hoods use aluminium mesh filters, with stainless baffles appearing on the wider canopy models. Aluminium mesh must never go in a dishwasher, where the strongly alkaline detergent oxidises it to a chalky grey that never recovers. Soak them flat instead.
The impeller is where the complaints come from
Take the filters out and look up with a torch. The impeller sits in a housing above, and everything the filters missed has been thrown against that housing and baked into a brown lacquer.
That single deposit explains almost every rangehood complaint. The smell is warm grease in a warm housing every time the fan runs. The noise is grease building unevenly on the blades, putting the impeller out of balance so a quiet hood develops a hum. The poor extraction is a loaded impeller simply moving less air.
On many Bosch hoods the impeller cover comes away with a few screws and the surfaces can be reached with a non-caustic degreaser and a cloth. On others the motor assembly is not designed to be opened by an owner, and forcing it achieves nothing useful. If the cover does not come off easily, clean what you can reach and stop, because a motor that gets wet is a worse problem than a motor that is greasy.
Isolate the power first, at the wall or at the circuit breaker if the hood is hard wired. An impeller starting while your hand is in the housing is a serious injury, and hoods are frequently wired to a switch that is not obvious.
What actually goes wrong
A charcoal filter that has never been replaced, on a recirculating hood in an apartment. The most common Bosch hood fault and it is not a fault at all.
Grey mesh filters from a dishwasher cycle.
An owner searching for a Bosch-badged replacement filter that is listed under a sibling brand.
A hum or rattle from an impeller loaded unevenly with grease, which no amount of filter cleaning fixes.
A hood switched to its lowest speed permanently because the higher settings became loud, which halves the extraction and doubles what lands on the cooktop and the wall behind it. The noise was the symptom, not the setting.
Should you do it yourself?
Do it yourself for the filters, every couple of months.
Get someone in for the impeller housing, or if the hood has developed a smell or a noise, or if you have never established whether it ducts outside at all.
Most people book it with the Bosch cooktop below and the Bosch oven under that, which is a very different job if it has EcoClean liners.