Cat urine smell returned after washing powder

The washing powder masked the smell temporarily, but it couldn't break down the uric acid crystals in cat urine — those crystals are what cause the odour to keep returning, especially in humidity. The only products that permanently eliminate pet odours are enzyme-based cleaners, which actually digest the organic matter rather than covering it. Biological detergents contain some enzymes, but they're not formulated for this job and they can't penetrate deep enough into carpet fibres and underlay. Before I point you to the right product — is this a single spot or a wider area, and do you know roughly how long ago the original accident happened?

That's a classic set-in stain situation — 8 months in, the uric acid has had time to really bond with the carpet fibres and likely penetrated the underlay too. Siberians are also known for producing quite potent urine, so you're dealing with a stubborn one. The good news is it's absolutely treatable. One thing worth knowing: has your cat been returning to that same spot since the smell came back? That'll tell us whether the area has been re-marked.

Completely understandable — and that re-marking is actually what makes enzyme cleaners essential rather than optional here. The product I'd recommend is Simple Solution Extreme Pet Stain and Odour Remover. It's a professional-strength enzyme formula specifically designed for set-in stains, and it's one of the most consistently effective products available for exactly this situation. For an old, re-marked stain like yours, the key is saturation — you need to soak the area so the enzymes reach the same depth the urine did, which means going further into the carpet than feels intuitive. Blot up as much liquid as possible first, apply generously, cover with a damp cloth to stop it drying too fast, and leave it for 10–15 minutes before blotting dry. Don't use any heat to dry it as that sets the proteins. You may need a second application given how long this has been there.

Good question — avoid steam cleaners entirely as the heat permanently bonds the proteins to carpet fibres. A cold-water carpet cleaning machine can be used, but only after the enzyme cleaner has had its full dwell time and you've blotted it dry. Don't mix the enzyme cleaner with anything else, including other cleaning products or fragranced sprays — anything that disrupts the pH will stop the enzymes working. Once you're confident the smell is gone, a very light spray of diluted white vinegar after the area has dried can deter your cat from returning to the spot.

That should crack it — just be generous with it and don't rush the process. The patience is what makes the difference with old stains. Good luck, and if the smell persists after two applications it's worth checking whether the underlay or floorboards underneath have been affected, as that sometimes needs separate treatment.