Owen Mor on the Culmore Road is closed to new admissions after inspections by the Regulation and Quality Improvement Authority (RQIA).
The home said the RQIA’s concerns do not relate to the delivery of care.
A specialist unit of the home closed last week due to staffing issues, management said.
In a statement Owen Mor management said they have been working with the RQIA and have been making “good progress” towards addressing the health watchdog’s concerns.
The care worker, who has asked to remain anonymous, told BBC Radio Foyle she eventually quit her job at the home because of “really low standards of care”.
She said: “There were no wipes, no dermal wash. The (incontinence) pads were either too big or too small. The very basic, very fundamental parts of care the residents need were severely lacking.”
She said training and support for staff was virtually non-existent, and when concerns were raised they were dismissed.
In a statement Owen Mor management said: “The regulators and the trust have been monitoring what it called the positive progress to reach compliance and enable the home to reopen to new admissions.
“At no time in all of this was there ever any concern about the standard of care and compassion given to residents.”
Some families of Owen Mor residents raised their concerns at a public meeting in Derry on Saturday.
One woman, whose mother lives with dementia, said her family have expressed concern over staffing levels and training in a series of meeting with the trust.
“In the early stages we were told it was teething problems in the enhanced unit but two years later things are still very concerning,” she said.
“We feel alone and abandoned,” she added.Last week the family of patient Joseph Stewart told of their heartache after finding their dad “sitting in his own dirt”.
Evelyn Hoy, of the Commissioner for Older People’s office, said she was dismayed to hear some of the relatives’ stories.
“It was extremely distressing to hear such familiar stories of families who have experienced terrible care and then tried very hard to complain and to have those complaints unheard by the authorities,” she said.
Ms Hoy said the commissioner Eddie Lynch met with the Western Trust last week. She said the trust were unable to give Mr Lynch an assurance that all residents were receiving safe and effective care.
The Western Trust said it is making “arrangements to meet families individually to listen to their experience and to respond in person”.
“This is also an opportunity to inform families about the detailed action the Trust has taken to date and to reassure them”, she added.
The 81-bed care home first came under the spotlight in May after an investigation.
Inspectors highlighted concerns about staff knowledge, including nurses not following policies and procedures, as well as inadequate records about patient safety, including falls, feeding and nutrition.
After a follow-up inspection in August, the regulator stopped new patient admissions after obtaining a court order.