The Hearing Association says it is unacceptable a problem with the emergency 111 text service used by the hearing impaired took 13 hours to fix.
The system allows people with hearing or speech difficulties to contact emergency services via text messaging. One to two emergency messages are received by the system each week.
The 1500 registered users were unable to access the service between 4.30am and 6pm yesterday.
About 15-hundred deaf, hearing or speech impaired people are registered for the emergency text service.
Police said the service was down because of a technical problem.
Hearing Association president Stuart Keene told Summer Report the mistake must not be repeated.
"They of course need to ensure that they have adequate staff of the right skills to fix the problems promptly.
"Thirteen hours is a very long time to fix what is most likely a computer glitch."
Mr Keene says the Hearing Association will look at promoting an alternative way of contacting the emergency service if another malfunction happens.
Disabled Persons Assembly chief executive Rachel Noble said the text facility was an extra layer of security and yesterday's outage caused her some distress.