I have cold & hot water downstairs. No cold water upstairs.Possibly a frozen cold water pipe.Is it safe to use central heating?

Yes, the warmer the better, the heating system is hot water pipes.
Go around with a hair dryer on any cold water pipes you can access, with cold water faucets open so you'll know when it's thawed. You don't want a burst pipe. You may have one, but you have to find out now or later anyway. Be prepared to shut off the main in a hurry.