My elderly cat keeps pissing on the doormat

[hillyhilly]

Our lovely Bombay Blue is 16, she is pretty fit and well, she has had a urine infection or two in the past year but is showing no signs of one at present, although she is drinking quite a lot and her urine is pretty dilute (thankfully).
During poor weather, she understandably doesn't want to go out but rather than use her clean, unshared litter tray, which she will use occasionally, she prefers to piss on our front doormat.

I've just put a new mat down, before putting it down I cleaned really thoroughly to try and get rid of any smell and sprayed the whole area liberally with feliway but the other morning, despite having a clean litter tray, she came in and had a huge pee all over it.

She's now done it again on a different section and despite it being a hard floor and no signs of pee, my kitchen smells of cat pee too.
This has been a recurrent problem for the past few winters and is really getting us down, we don't want visitors coming in to a cat pee stink.

I've sprinkled bicarb of soda all over the offending area - any further advice please?
I know that I could take her to the vets for a check but she gets very distressed by it and they want to take hugely intrusive tests on her bloods and kidneys which as well as being hideously expensive, would be distressing for her too.

This has been a problem for years when I think about it, we used to blame it on having two cats, now we only have one, we blame it on her age, I really don't think she has an infection which is why I'm avoiding the vet.
TIA

[chockbic]

Can you take a urine sample to the vet? They will be able to test it for infection without the invasive stuff.

When our girl peed outside her box, we put down a sheet of plastic with little bumps on. Apparently they don't like the feel of it on their pads.

Have you considered changing to a shallow tray? Change the litter to another type?

Its trial and error with them. Sometimes there's no rhyme or reason.