For the third day running, Tube services were interrupted by power losses in an unprecedented failure on the Underground.
Engineers still searching for the cause are checking 26 miles of cabling on the line between Liverpool Street and Ongar.
Early yesterday morning, empty trains were run as a test but the power failed again and London Underground decided not to attempt a service through fear that people would again be stuck in tunnels.
A spokesman said: 'It was not reliable enough for us to run a service and we did not want to risk it disrupting other services again.' Trains did operate on the rest of the Central Line between Liverpool Street and Ealing Broadway and West Ruislip.
On Wednesday, 20,000 people were stuck in 29 trains trapped by the power failure and many had to be led to safety.
London Transport has organised a fleet of 80 buses hired from operators as far afield as Oxford, Colchester and Ipswich to run an emergency service between Central Line stations until the service is resumed. Replacement buses yesterday were overwhelmed by demand.
There is a chance that the Central Line service could be restored this afternoon, but London Underground remained pessimistic.