In a statement, the broadcaster said: "On Saturday 25 September, the fire suppression system was triggered at Red Bee Media’s broadcast centre, which transmits all Channel 4’s services. As a result a large number of hard disks in a variety of systems were severely damaged. This significantly impacted the playout servers which meant that our channels and on-demand services were temporarily taken off-air.
We immediately activated our emergency back-up system, and while our channels are back on-air, we are still trying to fix some significant problems.
One of these is not being able to provide access services - subtitles, audio description or sign language support - for programmes broadcast since the incident.
We know that this is incredibly frustrating for you and your families who rely on these services to watch your favourite programmes.
The reason is that when we activated our emergency back-up, the system that should have provided subtitles failed. Since then, our engineers have been working around the clock to find out what went wrong and how we can fix it.
Unfortunately, at the moment we cannot provide audio description or sign language services at all. These services were irretrievably lost during the incident and we won’t be able to restore them until we move to the new system we are building.
So, we have focused on a solution for subtitles. This is a complex job, as a large number of different systems at Channel 4 and beyond have to talk to each other to make this work. Until now, all testing has been overnight as we couldn’t risk coming off-air again.
However, we are beginning to make progress. For example, some of you might have noticed we have been testing subtitles on More4 and Channel 4 during the day.
On Friday 15 October, we successfully had live subtitles during Stand Up To Cancer.
This week, we will begin to add subtitles for some of the programmes you have missed – Gogglebox, the Great British Bake Off and its Extra Slice – on All 4. However, 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.
The damage caused by the incident has meant that we have had to build a completely new system. Not only will this enable our channels to move back out of disaster recovery, but it also means we will be able to provide subtitles, audio description and sign language services as well.
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.
We know that this will be incredibly disappointing to everyone, but we do need to get this right. In the meantime we will continue to put our most popular programmes that you have missed, with subtitles on All 4."