Network Rail has confirmed that floodwater is likely to continue to affect trackside signalling and safety equipment for some time.
In a statement, they said: "While they work to fix the problem we will only be able to run five trains an hour between Paddington and Reading in each direction. This is around a fifth of the services that would normally be scheduled.
"This will continue until Network Rail lets us know it is safe to run a full service again. We strongly advise customers not to travel unless it is absolutely necessary, and to consider alternative routes."
More top news
Detectives investigating an assault in Newham have released CCTV footage in a bid to identify the two suspects who attacked a 23-year-old.
Concern is growing for the welfare of a 28-year-old woman who has not been seen for more than two weeks.
A police officer in today's London Pride parade surprised his partner by proposing in the middle of the parade.