The crisis severely affected 76 GP practices across Bradford leading to a huge backlog of work.
Clinics were disrupted as the emergency lasting more than three weeks caused delays making routine hospital referrals and affected tests, results and prescriptions.
An independent review of the incident said many surgeries turned to fax machines to send fast-track referrals to specialists but some no longer using the technology relied on staff collecting paper forms for delivery directly to local hospitals.
Health and Social Care Secretary Matt Hancock has ordered NHS chiefs to scrap fax machines by next March but the report warns officials need to consider alternatives in case of future breakdowns.
It reveals the risk of major IT failure at the former headquarters of Bradford’s NHS clinical commissioning groups (CCGs) was well known.
But officials took more than five years to agree changes, with approval for a £3 million business case required from six separate layers of NHS bureaucracy.
Two previous breakdowns in air conditioning equipment led to significant disruption including in 2015 when key IT servers were shutdown to prevent them melting.
A third failure in October came as servers were part way through transferring data to a new base at Huddersfield Royal Infirmary.
Officials decided to bring forward the full transfer, but new problems emerged which required extensive repairs to systems, severely affecting GP practices.
The crisis escalated over following days as issues including loss of email persisted forcing NHS chiefs to declare a serious incident.
Difficulties were further exacerbated when an unrelated telephone helpline fault hampered surgeries from contacting IT experts for four days.
NHS officials offered GP practices £1,000 each in compensation amid mounting frustration and anger among staff.
The report says recovery was affected by confusion over responsibilities.
IT support was provided by a consortium of private firms hired to deliver back office services to the local NHS but the review said it had not been provided with evidence of a “disaster recovery plan” for an emergency, noting “essentially it appears to have come down to reliance on good people who knew what to do”.
It also found CCGs and GP practices had not drawn up effective plans for business continuity during a crisis.
The report said the delay tackling the risk of IT failure at the CCGs’ headquarters was “unacceptably long”, linked in part to new working arrangements following the Government’s controversial shake-up of the NHS in 2013.
The report added: “The system was not ready for this incident but responded well to the crisis.
“It could however have been better prepared, particularly given the previous incidents. System resilience was never quite the priority that recent events have demonstrated it was.”
Making 17 recommendations for changes, it said better planning was needed for future failures of critical infrastructure.
“Fax machines were used for urgent referrals during the outage period…with their phase-out nationally, consideration is needed to understand alternative methods in an outage,” it added.
In a statement, the three Bradford CCGs said a separate review had found no patient harm from the incident and no data had been lost. An action plan was being implemented.
“Our main focus was to ensure that people in the area continued to receive a high quality, safe service when they visited GP practices,” they said.
“GPs were able to see and update patient records and had systems in place to manage urgent and fast-track referrals. Patients continued to be seen.”