It is important that he is checked by a vet for any related medical problems. If he gets the all clear it may be that for some reason he feels threatened and wants to increase his sense of security. Perhaps there is another cat making a move through his territory? You don’t say whether he is spraying (standing up and squirting urine) or squatting just releasing it as he would if he was just having a wee. It is also important to see whether he is straining at all and this will have to be looked into by your vet.
You could try increasing his sense of security by taking a towel that he has slept on and using it like a duster to spread more appropriate scent around the places he generally urinates on.
Hope this answers your question
Rosie Barclay