St John's, in Ranmoor - one of the city's biggest churches - had to close last October after part of the Grade II* listed building's 130-year-old painted ceiling broke off.
Scaffolding has been put up throughout the building, evening prayer and communion have been moved to the nearby Ranmoor Parish Centre, and full choral services and musical recitals have been affected too.
A provisional date of February 14 was initially set for the reopening, but churchwarden Brian Parfett said there was 'no way' this could be met.
"We don't know when it's going to reopen," he said. "We felt we needed to give a date to help people, but things take longer than you anticipate, particularly when you've not experienced it before."
Specialists were called in to investigate and the root of the damage has now been confirmed. The plasterwork on the panels has 'debonded', breaking away from the wood beneath. Brian said each of the ceiling's 350 panels had been coated with a mixture of cow hair, lime and sand to prevent cracking.
"We believe, 130 years ago, there was an outbreak of anthrax, so instead of using horse hair they used cow hair instead. It's not that that's caused the problem, it's fine apparently."
Water has leaked in places but the precise cause of the collapse 'hasn't really been determined', he added.
As the building is listed, special consent is needed to carry out work and it must be restored to its original condition. The cost of the necessary repairs will not be known until the chosen architect provides a list of options.
"People have started to give us quotes. We will have to find the money somehow. We're looking at grants but often it takes a long time to get funding through," said Brian. "We don't want to have the church closed for a long period of time."
The Church of England could provide emergency money, he said, and St John's has its own reserves to dip into.
"Until we know the costs and can actually describe what we're going to do, we can't really apply for grants."
He said the situation highlighted a 'dilemma people face throughout the country'. "A lot of historic buildings are in the hands of a small number of people who are passionate about them, then something like this happens and they have to find the money. Because it's wear and tear it's not covered by our insurance. If it had been recent water ingress that could assist us with a claim but this isn't, it's just regarded as age."
Brian said services had been 'pretty good' at the Parish Centre, with 105 worshipers attending last Sunday's communion led by the Bishop of Sheffield, the Rt Rev Dr Pete Wilcox.
St John's is a popular wedding venue, and 26 ceremonies were booked in this year. People can get married at neighbouring churches, if they wish, said Brian. "That's what most couples are considering doing."
The present building dates from 1888 and is the second Anglican church to be built on the site off Ranmoor Park Road. The original was almost entirely destroyed by fire in 1887, leaving just the 200ft tower and spire, the tallest of its kind in Sheffield.