After a long time suffering of sub-optimal fan extraction in my kitchen, I decided to go to the root of whatever was causing it. I have a Zanussi ZHC60136X. I clean the filter grids every now and again (~6 months?) but haven't done any other maintenance on it. I had the impression that the fan was blowing, instead of sucking, and after removing the filters, it's quite obvious that it's venting air out. I did the usual test for this, placing a pot of steaming water on the hob and see if the stream of steam gets sucked when the fan is on: there is not much difference between turning the fan on or off, and some of the steam escapes the hood without being sucked by the fan.

After checking the manual, I saw that there were meant to be some coal filters attached to the air inlet. I thought that the filters must have been saturated and needed replacement, but after disassembling the inlets, I realised that there were no carbon filters at all! There has not been any since I moved into the house (two years and a half ago) and I doubt they were before (the house is around 4-5 years old). The fan seems to work nicely, so the grease has not affected it much even with the absence of filters.

My motor assembly lacks the carbon filters

Could it be that the lack of carbon filters is affecting the way the fan works, making it blowing instead of sucking air? Is it too late to fix now, could the vent be blocked somewhere upstream, where I can't clean it? I don't run a chicken shop, the motor assembly was dirty, with some grease as you would expect, but is not a clusterf*** of grease.


  • You seem to contradict yourself in the first paragraph with "... it's quite obvious that it's venting air out. Steam from a pot doesn't get sucked to the hood ...". Please edit to clarify.
    – isherwood
    Aug 8, 2017 at 16:40
  • I meant that the fan is pushing air out of the duct, instead of sucking it. It's quite frequent to test it with a pot of steaming water. When you turn the fan on the stream of steam should be sucked by the hood, but there is not much difference between the fan being on and off. I was thinking that the carbon filters might change the dynamics of the duct/fan system. That's what led me to think that when they are on, the thing would work properly, and when they are off, the fan "seems" to push air out, instead of sucking it in. I will double check the wiring, and report back. Thanks! Aug 9, 2017 at 11:13
  • I am also in sure where the fan is moving air. It is possible there is a back draft damper above the fan that is sticking. These can be harder to get to and are small usually metal plates the fan blows open when on, when the fan turns off they drop back in place just a little grease buildup can cause them to stick closed or partly closed.
    – Ed Beal
    Dec 28, 2017 at 14:11

3 Answers 3


buy yourself an endoscope and send it up the vent so you can see what is going on. probably clogged


Joel, the carbon filters are to help stop grease from getting to duct work. We had a similar issue feeling cold air down draft in winter, warm in summer. Our duct work had given out. Easy fix to replace and we took out the flex pipe installing solid duct pipe. But if it blows in when the motor is on, find a manual on line, it may have been installed incorrectly


Sounds to me as though the duct is blocked, most likely a damper / flap that is stuck closed by grease buildup. With a blocked duct, the fan may spin, but there would be no air movement.

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