Channel 4's ability to provide subtitles, signing and audio description services are not going to return for at least another month, despite them being knocked offline in September.
The outage started on September 25 and has already led to hundreds of complaints to Ofcom from deaf and visually impaired viewers and listeners.
Ofcom said they were "extremely concerned" about the impact it would have on people who used the services.
Channel 4 said the fault happened when the fire suppression system was triggered at the Red Bee Media’s broadcast centre.
As a result, a large number of hard drivers were damaged, which "significantly impacted" their services
They said their ability to provide audio description services and sign languages were "irretrievably lost."
Backup systems were turned on but they failed, they added.
Channel 4 said: "We know that this is incredibly frustrating for you and your families who rely on these services to watch your favourite programmes."
In the days after the incident, Channel 4 was beset by numerous technical issues which impacted viewers ability to watch the shows.
At the start of October, viewers reported on social media that they had experienced sound and picture issues with the broadcaster’s output.E4 also apologised after airing a repeat episode of Married At First Sight UK instead of the series finale.
They have now committed to building an entirely new subtitles and assisted viewing system but will not be able to provide any similar services until it is finished.
Since the incident, some shows have now regained subtitles but Channel 4 said it wouldn't be able to provide a complete service until mid-November at the earliest.
They said in a statement published on Thursday: "We have been rebuilding the system over the last few weeks, and there is still a considerable amount of work to be done. We cannot rush this and run the risk of something going wrong.
"Something like this needs to be installed slowly to ensure our channels don’t come off air and to prevent something like this happening again.
"That means that full access services might not be available until the middle of November. Clearly, if we can do anything to speed up this process, we will.
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Assisted viewing will be available for key shows like The Great British Bake Off and Gogglebox on All 4, but they said "this is a very labour-intensive process, so it isn’t possible to make every programme available simultaneously.
"We know this isn’t good enough, but it’s a start."
An Ofcom spokesperson said: "We remain extremely concerned by the impact on people who rely on these services. Channel 4 did not have strong backup measures in place, and it should not have taken several weeks to provide a clear, public plan and timeline for fixing the problems.
"We now expect Channel 4 to meet the timings it has set for restoring these vital services."