Why won't my filters come clean?

Usually because the grease has baked on and hardened (so ordinary washing can't shift it) or the filter is worn out (damaged mesh holding grease that won't release); the first needs a proper hot degrease, the second needs replacing - work out which. Canopy filters won't come clean, however you wash them, for one of two usual reasons. First, baked-on, hardened grease: grease repeatedly heated (by the hot air drawn through and any flare-ups) hardens into a tough, varnish-like deposit bonded to the filter, which ordinary washing (a quick soak, a scrub, a dishwasher cycle) can't shift. This needs a proper hot degrease - a long soak in a hot grease-cutting solution, or professional cleaning - to soften and release it. Second, a worn-out filter: a filter whose mesh is crushed, bent, corroded or clogged solid holds grease in its damaged structure that won't release however you clean it, because the mesh itself is degraded. A worn-out filter can't be restored and needs replacing. So work out which you've got: if the filter's sound but the grease is hardened, clean it harder; if it's worn out, replace it. So it's baked-on grease or a worn filter. So because the grease is baked on, or the filter is worn out. This is general guidance.

With a proper hot degrease - a long soak in a hot, grease-cutting solution to soften and release the hardened grease, or professional cleaning; ordinary washing won't shift baked-on grease because it's too hard, so it needs the hot soak, then clean more often to stop it recurring. You clean baked-on grease off a filter with a proper hot degrease - not the ordinary washing that failed. Baked-on grease is hardened, varnish-like, and bonded to the filter, so a quick soak, a scrub or a dishwasher cycle can't shift it. What works is a long soak in a hot, grease-cutting solution: the heat and the degreasing chemistry soften and release the hardened grease over time (a proper soak, not a quick dip). Professional cleaning does the same with the right chemicals and equipment. So the method is: submerge the filter in a hot degreasing solution and leave it long enough for the grease to soften, then it should wash off. Crucially, once it's clean, clean it more often going forward - baked-on grease means it was left too long between cleans, so more frequent cleaning (while the grease is still soft) stops it baking on again and coming to this. So the fix is a hot degrease now, and regular cleaning after. So soak it hot and long in a degreaser, then clean it regularly. This is general guidance.

It won't come clean even after a proper hot degrease, and the mesh is physically damaged - crushed, bent, corroded, or clogged solid; a sound filter under the grease is smooth intact metal, a worn one is misshapen, rough or permanently blocked - if it's damaged and won't clean, replace it. You know a filter is worn out when it won't come clean even after a proper hot degrease, and the mesh is physically damaged. The test is: give it a proper hot soak in a grease-cutting solution (the treatment that shifts hardened grease); if it still won't come clean, and the mesh is damaged, it's worn out. Look at and feel the filter's condition: a sound filter (just greasy) is smooth, intact metal under the grease, with its shape and mesh good; a worn-out filter is misshapen (crushed, bent), corroded (rough, pitted), or clogged solid (grease permanently set in the blocked mesh). A worn filter holds grease in its degraded structure that won't release, because the damage is physical, not just grease. So the signs are: won't clean even after a proper degrease, plus a crushed, corroded or solidly clogged mesh. A worn filter also captures grease less well, so replacing it restores function too. So if it's damaged and won't clean, replace it (see the when to replace vs clean a filter page). So it's worn out if it's damaged and won't come clean. This is general guidance.

No - a worn-out filter has physical damage (crushed, corroded or clogged mesh) that holds grease and won't release however you clean it, even with a proper degrease; the damage isn't grease you can wash off, so it can't be restored and needs replacing. No - a worn-out filter can't be cleaned back to good. The problem with a worn-out filter is physical damage, not just grease: the mesh is crushed flat, bent, corroded rough, or clogged solid with grease set hard in it. This damaged structure holds grease that won't release however you clean it - even a proper hot degrease won't restore it, because you're not dealing with soft grease you can wash off, you're dealing with a degraded filter. So washing, soaking, scrubbing or degreasing can't bring a worn-out filter back to clean; the damage is permanent. A worn-out filter also captures grease less effectively (a damaged mesh works less well), so even if you could get it looking better, it wouldn't do its job properly. So a worn-out filter needs replacing, not cleaning. The good news is filters are replaceable and not usually expensive, and a new one, cleaned regularly, will come clean easily and capture grease well. So no - replace a worn-out filter rather than trying to clean it. So no; it needs replacing. This is general guidance.

Usually because they're not cleaned often enough - grease left on the filter is repeatedly heated and hardens between washes; cleaning them more frequently, while the grease is still soft, stops it baking on hard, so they come clean easily. Your filters keep baking on grease usually because they're not being cleaned often enough. Grease on the filter is repeatedly heated - by the hot air and steam drawn through, and any flare-ups below - and repeated heating hardens it. If the filter's left between cleans, the grease has time to bake on hard (into a varnish-like deposit) before you next wash it. So it won't come clean, and the cycle repeats. The fix is to clean the filters more frequently - often enough that the grease doesn't have time to bake on hard between washes. Filters cleaned regularly, while the grease is still a soft film, come clean easily; filters left until the grease hardens don't. How often depends on your cooking (heavier, greasier cooking needs more frequent cleaning), but the principle is: clean before it bakes on, not after. This also protects the ductwork (a clean filter catches grease better) and extends the filter's life (grease left on hardens and wears it). So they bake on because they're left too long - clean them more often. So because they're not cleaned frequently enough. This is general guidance.

Only if they're worn out - try a proper hot degrease first; if that cleans them, they were fine and just needed a stronger clean (then clean more often), so don't waste them; replace only if they're damaged and won't come clean even after a proper degrease. Not automatically - only if they're actually worn out. Before replacing filters that won't come clean, try a proper hot degrease first (a long soak in a hot grease-cutting solution, or professional cleaning). If that cleans them, they were structurally fine and just had baked-on grease that ordinary washing couldn't shift - so replacing them would have been wasteful. In that case, keep them and clean them more often going forward (so grease doesn't bake on again). Only replace a filter if it's genuinely worn out: physically damaged (crushed, bent, corroded) or clogged solid, and not coming clean even after a proper hot degrease. A worn-out filter can't be restored and does need replacing (and captures grease less well anyway). So the order is: try a proper degrease first; if it comes clean, keep it and clean more often; if it won't come clean and it's damaged, replace it. So don't replace a sound filter that just needs a stronger clean, but do replace a worn-out one. So replace only worn-out ones - degrease the rest. This is general guidance.