A spokesman said: "We've brought a new delivery partner onboard, but they've had a couple of teething problems.
"Getting fresh chicken out to 900 restaurants across the country is pretty complex!
The Colonel is working on it. pic.twitter.com/VvvnDLvlyq— KFC UK & Ireland (@KFC_UKI) February 17, 2018
"We won't compromise on quality, so no deliveries has meant some of our restaurants are closed, and others are operating a limited menu, or shortened hours.
"Shout out to our restaurant teams who are working flat out to get up back up and running again."