Vulnerable older people endure shocking conditions in the private rental sector, leaving them at risk of neglect, bullying and abuse, according to Age UK.
The charity warns that, with growing numbers of people renting into their old age, urgent reforms are needed to make sure older tenants are not living in "squalor".
It has seen cases involving privately rented homes with only an outside toilet, homes with broken boilers and leaking taps and homes left without cooking facilities for months.
Some family members of those renting told Age UK they thought the landlord was waiting for the tenant to die before taking action to improve the property.
Calls to Age UK's advice line between 2013 and 2016 revealed that at the bottom end of the rental market, some tenants were living in damp, mouldy and cold conditions - potentially making health problems worse.
Some tenants feared eviction if they challenged their landlord over the poor conditions and there were also reports of over-the-top rent rises being imposed if necessary improvements were made.
Age UK has also seen cases of landlords refusing to allow the installation of aids and adaptations, such as ramps or handrails, needed by some older people.
Older tenants also said they were feeling harassed and bullied into leaving a property because their landlord wanted to sell.
The charity wants to see more resources for local environmental health services, better access to adaptations for older people and more housing advice made available.
Caroline Abrahams, charity director of Age UK said: "Calls to our advice line show that some highly vulnerable older people are enduring grim living conditions in the private rented sector and this is truly shocking.
"No one should have to put up with such squalor at any age, but the idea that a chronically ill older person could be living on their own for weeks or even months with no proper heating, or cooking facilities or hot water is sickening.
"The law is far too feeble and the withering away of local environmental health services is making the problem worse. The upshot is that older tenants in the private sector are almost entirely reliant on the decency and professionalism of landlords and letting agents, and sadly this is leaving some at risk of neglect and in the worse cases of bullying and abuse."
She said the poor practice that older people have described to Age UK "is an embarrassment to the many decent private sector landlords".
In one case seen by Age UK, a woman with health problems who had lived in the same rental property for over 50 years had a broken boiler and a leaking tap that caused occasional flooding.
In another case, a housebound man was renting a home with an outside toilet and no bathroom, with the only running water being in the kitchen and the only heating coming from an electric radiator. He was paying £590 a month.
In another case seen by Age UK, a man was left without cooking facilities for several months.
The charity has also spoken to a man with terminal cancer, who paid for improvements to his rented home himself as he did not want to "rock the boat".
Commenting on the findings, Chris Norris, head of policy at the National Landlords Association (NLA), said: "There is no denying that a small proportion of landlords fail to meet their obligations towards their tenants, regardless of age or wellbeing.
"This is unacceptable and the NLA would like to see local authorities and enforcement agencies take a harder line with poorly performing landlords, who give professional providers of housing a bad name.
"Unfortunately, many older households are much more likely to have tenancy agreements which pre-date increased protections for tenants that were introduced in the late 1980s."
He said that, with taxation changes pushing up landlords' costs, there was concern that more households reliant on the private sector would not be able to find the homes they needed, "potentially forcing them to leave communities they have known and contributed to for decades".
A Department for Communities and Local Government (DCLG) spokesman said the Government is determined to protect the most vulnerable people.
He said: "We've given councils £12 million to crack down on rogue landlords, with nearly 70,000 properties inspected and over 5,000 landlords facing further enforcement action or prosecution.
"We're also introducing banning orders, fines and blacklists, and have introduced legislation to protect tenants from being evicted when they have a legitimate complaint about a property."