Aged Concern Canterbury is warning of cases where elderly people have felt unnecessarily pressured to replace expensive heat pumps.
The charitable organisation's chief executive, Simon Templeton, said they were aware of five cases in Christchurch in which elderly people who had requested a heat pump clean were then told they needed a new machine.
Mr Templeton said people were ending up with a working heat pump, but they were being pressured with a hard and quick sell.
In two cases the original heat pumps were later found to be still functioning, he said.
He feared there were many more cases, and advised elderly people not to accept visits from cold callers, Mr Templeton said.
In May, 82-year-old Roger Greening had a call from a company representing themselves as Powersmart, a company he had dealt with before, telling him he was due for a service.
The service technician visited and said he was using a new steam technique to clean the machine.
Three weeks later the machine stopped working. Mr Greening called the technician but was directed to call another company, Ocean HeatMaster, who would check the machine.
He said Ocean HeatMaster said the outside machine was broken, and it would cost almost $3000 fix it, but he could buy a new one for $3500, which could be installed the next day.
Mr Greening said he felt pressured to take up the offer, and decided he couldn't go without the heat the machine provided.
He said he now regretted buying the heat pump without checking the situation out further.
Powersmart's manager said they were not the company which serviced Mr Greening's heat pump or referred him to the second company which sold him the heat pump.
The company said they believed someone was falsely using their name, and they were looking into their legal options.
Ocean HeatMaster, which installed Mr Greening's new heat pump, said they stood by the diagnosis of the fault. They said they still had Mr Greening's machine, and he could have it back for a second opinion if he wished.