Harry signed up for a boiler, solar panels and energy saving lightbulbs after a salesman turned up at his door flogging a half price offer.
The cost of the energy efficiency package was £1650 but an alleged Government grant under the Green Deal meant the cost reduced to just £800.
But the pensioner later discovered he was tied in to a credit agreement for £10,000 over 23 years.
Harry, 75, said: “I thought I couldn’t lose as I needed new heating and the grant made the cost a lot easier to manage.
“I had no financial constraints and no mortgage as I’d paid it off when I retired.
“You have to trust people and I trusted that salesman. Now I wish he had never darkened my door.
“I’ll be nearly 100 by the time this is paid off.”
The retired joiner, of Maryhill, Glasgow, signed up in December and had no idea the Green Deal scheme had ended in July.
Once the system was installed, he was shocked to be hit with the £10,000 bill.
He said: “I started to look at the paperwork.
“I had read it before signing but there was so much of it that I gave up halfway through. I want to warn others to be wary.
“The solar panels were also supposed to be a no brainer and reduce my heating and lighting bills.
"But there has been no difference at all in my outlays every quarter except that I am lumbered with this debt.”