Have you laid a new floor, cupid? You've changed his habitat - perhaps there is a smell in the new kitchen which is not nice to a cat, glue or something like that. Pick him up and carry him into the kitchen, talking soothingly - then take him back into the front room again. Does he have to go through the kitchen to go out to poo? - he needs to know that he is still safe to do that, you don't want him sneaking off somewhere indoors to poo if he feels the kitchen is too scary.