Channel 4 is being hit by rising complaints about technical problems cutting people off from popular shows including The Great British Bake Off and Gogglebox.
After a long outage, subtitles have returned to many Channel 4 shows - but signing and audio descriptions are still not available on its channels and some viewers say subtitles have been fauilty.
And Ofcom says it is considering taking action against the broadcaster to ensure this does not happen again.
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The outage started on September 25 when subtitles, signing on audio description services were knocked offline for Channel 4, E4 and 4Music after a fire suppression system was triggered at Red Bee Media's studio.
Red Bee supply the subtitles and access support for both Channel 4 and Channel 5. Back up systems were activated by Channel 4 but failed.
In a statement, Ofcom said: “We remain deeply concerned about the scale of the technical failures experienced by Channel 4 and the length of time taken to fix them.
“These problems have caused deep upset and frustration among people who are deaf, hard of hearing, blind or partially sighted.
“Channel 4 did not have strong backup measures in place. It should not have taken several weeks to provide a clear, public plan and timeline for fixing the problem.”
Also added: “We expect Channel 4 to meet the timings it has set for restoring all its services. When this is done, Ofcom will review the equipment and facilities that Channel 4 had in place.”
“We will consider what action might be required. We want to make sure broadcasters do not find themselves in this situation again. And so that subtitles, signing and audio description remain reliable even when problems occur.”
Each week Great British Bake Off fans take to Twitter to share their frustration over the technical issue.
One fan Twitter: "There were no subtitles again for Great British Bake Off and I struggle to hear the TV some of the time. When will this be fixed?
Another viewer added: "@Channel4 what is happening with the subtitles? No subtitles for weeks now! Is there an update as to why they have gone and when they'll be back?"
One said: "This is still not completely sorted. Escape to the chateau has half-formed sentences and non-coherent subtitles. #deafpeoplematter."
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