Complaints resolved against letting agents to the Property Ombudsman soared by 11% to 2,212 last year.
And two out of three were supported by the ombudsman.
The top causes of complaints were bad management; poor communication and record-keeping; arguments over the terms of tenancy agreements, dealing with deposits and inventories; and unsatisfactory in-house complaints procedures.
Landlords accounted for 49% of the 2,165 complaints received by the ombudsman in 2017 – a rise of 8%.
Most complaints concerned private rented homes in London (23%), with the South East (20%) and North West (11%) the regions recording the other highest levels.
Complainants were awarded an average £625.
The ombudsman’s report claims 14,692 letting agents or 85% of the sector are part of the scheme.
Property Ombudsman Katrine Sporle said: “We agree with government that there are gaps in the current provisions of consumer redress within the property sector which need addressing and, together with industry and consumer partners, we are keen to play our part in regulation and redress reform.
“Overall, 2017 represented a positive year of innovation and improvement, which will reassure consumers and the industry that there is an alternative to costly and lengthy court proceedings that can be relied on to provide timely, fair and reasonable remedies.”
The government wants to pare down the property ombudsman service from three groups with slightly different remits to a single ombudsman.
There are currently three schemes: The Property Ombudsman, Ombudsman Services Property and The Property Redress Scheme.
The ombudsman to which someone needs to complain depends on which redress scheme the company you’re complaining about belongs to.
Former housing secretary Sajid Javid said: “From broken boilers to cracks in walls, the current choice of schemes risks leaving thousands without answers, with others having to manoeuvre between different services just to work out where to register a complaint.
“Fixing this housing crisis is about more than just building homes, it’s ensuring people have the answers available when something goes wrong.”