7 month old pup started to wee indoors again.

As the title says, my 7 month old spaniel has been excellent indoors- never wetting and asking to be let out when he needs to go, but this weekend he has wee'd indoors four or five times!
A couple of times I can believe he has been caught short but twice he's done it when put the other side of the stairgate (as the cat was eating) and at least once he did it on the floor when there was someone else in the room (although it was my 8 year old and he was glued to the computer).
Should I be worried?

could be a bladder infection, need to eliminate medical reasons before seeking any behavourial issues, you need to clean the area with a proprietary cleaner in order to eliminate any trace of urine.
I would not worry myself.