House-trained dog started crapping in house

[MagdalenLaundry]

5 years old.
Stayed at dog sitters house while we were away. Stayed loads of times before
Crapped everywhere
Home and is doing the same here
Do I put into crate and start retraining

vet first to see if dog is ill.

Start watching him more and putting him outside. But I'd go to the vets first to rule out any medical issues.

Deffo take him to the vets

Dogs don't start doing this for no reason.

I wouldn't rule out stress.
Did anything happen differently at the dog sitters this time? - change of food/ other dogs / visitors he wasn't keen on....
He back in the same routine as before you went away?

The dog is either ill or stressed. Possibly saw another dog going to the toilet indoors and started doing it at the dog sitters house because of that.

Take it to the vet and then start toilet training again as if the dog is a new puppy. Feed the normal food at the normal times and your dog should get back to normal very soon.