The NHS 24 service is suffering from management failures at every level, according to an official report.
Call procedures are said to be bureaucratic
The review was published on Thursday and cited chronic staffing problems and a need for 90 extra call centre nurses.
It also criticised a lack of cohesion between Scottish health boards and NHS 24 and referred to complicated staff rotas involving 300 shift patterns.
Health Minister Andy Kerr welcomed the report and said steps were being taken to address some of the issues raised.
NHS 24 offers round-the-clock advice and support to people with health concerns and has been subject to a service review, commissioned by the Scottish Executive earlier this year.
NHS 24 Chief Executive John McGuigan offered an immediate public apology following the release of the report.
He said: "Since the autumn of 2004 it became clear that patients have had to wait too long for their call to be dealt with and the length of time that some patients have waited to be called back is unacceptable.
"I would like to apologise to those patients who have experienced a poor level of service."
Mr Kerr also announced the appointment of a new NHS 24 chairman following Christine Lenihan's departure last week.
The vice-chairman of Tayside Health Board, George King, is set to take over the role on an interim basis with immediate effect.
The interim report was led by former Ambulance Service chairman Owen Clarke and had an initial remit to improve NHS 24 service levels and staffing problems.
The team is due to deliver a final report on the service to ministers in September.
In the meantime, the main recommendations were:
- With call centres in Clydebank, South Queensferry and Aberdeen running at about two-thirds of planned staffing levels, the service must urgently examine the feasibility of the such sites
- Staff and management must find ways to reduce the time taken in finding out the health problem related to a call
- Find ways of simplifying the complicated shift patterns for workers to a more manageable level
- Senior NHS management must take a more hands-on role and focus primarily on helping solve the service's problems over the next 12 months
- Senior management must find time talk and listen to the concerns of front-line staff
- The executive should strengthen the management resources within the service with closer collaboration needed between health boards and NHS 24 staff.
Mr Clarke said despite the problems his team had delivered a high level of service and had the potential to deliver a "first-class service".
However, he added: "There are some major challenges and several parts of the service need to improve markedly - and quickly.
"One problem has been that expectations of what NHS 24 could achieve were not always deliverable.
"Although the overall design capacity is sufficient, there are problems with peak demand outstripping ability to respond.
Andy Kerr said moves had already been made to address the problems
"If concerted action is taken at all levels to address the interim recommendations, I am convinced that real progress can be made."
Mr Kerr said the report had highlighted the "significant challenges" facing NHS 24 and pledged to confront problems "head-on".
He said: "NHS 24 has already taken steps to address some of the issues raised but further action will be taken by the executive, NHS 24 and health boards to deliver change based on these interim findings.
"NHS 24 is here to stay as an integral part of the NHS.
"There are challenges that require to be addressed but I want to record my thanks to the dedicated and hard-working staff of NHS 24 who are putting an enormous amount of effort into delivering necessary changes and providing a valuable public service."
The Scottish NHS Confederation, of which NHS 24 is a member, said the review raised issues which were relevant right across the health service.
Director Hilary Robertson said: "Expectations can be very high when any new service is launched, on the part of those setting up the service, as well as those running it and using it.
"A vital part of developing a new service is being realistic about its ability to deliver on such expectations and recognising when expectations are unrealistic.
"A clear understanding about what support is required to make sure the service achieves what is intended, what risks are involved and how these will be tackled is also needed at the outset."
The British Medical Association's (BMA) Scottish General Practitioners Committee said the findings were a fair analysis of the problems affecting the service.
Its joint chairman Dr David Love said: "It bears out some of the concerns that GPs have raised over the past year about NHS 24 and clearly demonstrates that their concerns were entirely justified.
"We are pleased the problems are now being openly acknowledged and that we have the opportunity to consider in detail the reasons for the failure.
"The priority now is to get NHS 24 fixed for the future."