We don't have a cat.
I have 2 dogs. One of them has an occasional accident (usually about once a week). If this is through the day I wet vax it immediately with an enzyme based pet stain cleaner and then spray white vinegar on it. If it's on an evening and thus too late to switch on the noisy vax I soak as much of the patch up with paper towels as I can. Soak it with the enzyme cleaner and draw a chalk line round it so I can Vax it the next day. This has always worked.
About once every 2 weeks I move all the furniture and vax every room the dogs are allowed in just to keep the stale dog smell at bay. Again this has always worked. The house normally smells of pet stain cleaner, which I spray liberally around the house daily because I like the smell of it.
One day I came downstairs and there was a really over powering smell of ammonia. It didn't come on gradually, so I don't think it's the dogs. It happened over night.
I do leave windows open so I suppose a tom cat could have broken in and peed, but the terrier would have caused chaos so I'm not even sure that happened.
I've owned tom cats before. Anyone who has owned tom cats would know the stench is unmistakable.
I cannot for life of me find the source of this smell. It happened 3 days ago. Since then I've moved all the furniture and vaxed the entire floor with enzyme cleaner daily. I've washed all the skirting boards with disinfectant. I've washed the dogs beds. I've waited until the carpet is dry and the used neutrodol carpet powder, left it down for an hour before hoovering it up. Ive done this daily for the last three days. The smell is still there.
It is taking over my life. I need it gone before I totally lose my sanity.