Casper started to wee in the house again when he was about a year old.

(He had been house trained by about 11 weeks old.) We just had to go back to basics; taking him outside at regular intervals, waiting for him to perform and treating and praising when he did go outside.
Casper was also reluctant to go outside and didn't like treading on our grass.

I put his lead on and walked him around the garden until he weed. It only took him three days to realise the sooner he went, the quicker he got back inside.
I know how frustrating/annoying it can be be though - I threw one of our settees out as he peed on it and the smell was awful.