A rising number of people are in "debt denial" and fail to seek help for mortgage repayment difficulties, the financial ombudsman has said.
The service said it had received a record number of complaints about mortgages, despite the fact that repossession numbers were falling.
The ombudsman said that it only upheld about a third of complaints.
Some borrowers were making unrealistic appeals to lenders and sought help too late, it said.
The financial ombudsman deals with disputes that cannot be resolved between a financial services firm and a customer.
The service received 13,659 complaints about mortgages and secured loans in the past year - a record high and up from 12,845 in the previous 12 months.
About 40% of cases involved homeowners who were struggling with repayments.
This is only a fraction of all homeowners who have fallen behind on their mortgage repayments.
Figures published by the Council of Mortgage Lenders (CML) showed that 138,200 mortgages had arrears of more than 2.5% of the outstanding balance in the first three months of this year. This was the lowest level for six years.
The increase in complaints might relate to greater awareness of the ombudsman.
But the chief financial ombudsman, Tony Boorman, said that - for thousands of people - it was important to ask for help and guidance about arrears sooner rather than later.
"Mortgages are the most significant purchase most of us will make in our lives, so we understand why people might be reluctant to say that they're struggling to pay for their home," he said.
"Many of the cases where people face losing their home have been heart-breaking to deal with, but could potentially have been avoided."
He added that some homeowners were being unrealistic by asking for debt to be written off or for interest to be suspended indefinitely.
However, lenders could be "more creative" in ways of getting people back on track with payments, he said.