All vouchers for England's boiler scrappage scheme have been claimed but less than half of the money has been paid out so far.
All of the 125,000 vouchers that take £400 off the cost of replacing an old boiler with a new efficient one were claimed by 26 March.
Some 58,177 people have received the £400 rebate after paying up-front to have the work done.
A scheme is also operating in Wales and one will start in Scotland on 24 May.
The boiler scrappage scheme was announced in the pre-Budget report and was aimed at kick-starting the industry, which had suffered during the recession.
Households that had a G-rated boiler as the main boiler to heat their home were eligible to apply for a voucher to reduce the cost of an energy-efficient replacement.
People then shopped around for quotes for the new boiler and sent details of their chosen installer and product to the Energy Saving Trust (EST).
The EST would send a £400 voucher in return, but the householder needed to pay for the work up-front and then send the receipt and voucher to the EST. The money would then be put into their bank account.
The EST has told the BBC that all vouchers were claimed by 125,000 households by 26 March.
Of these, 97,283 have had the work completed and have sent in details to the EST.
A spokesman said that the target was for people to get £400 put in their bank account within 25 working days of these details being received.
So far, 58,177 have been paid the rebate, with the remainder being processed.
Householders have a deadline of 12 weeks for the work to be completed from when the vouchers are sent out.
More than 27,000 have yet to send in receipts for the work. The final vouchers were sent out about six weeks ago.
"We are sympathetic to allowing a few days leniency after the 12 weeks," an EST spokesman said.
Any vouchers that were returned unused would not be redistributed, he added. The scheme was now closed to new applications.
On the odd occasion, some householders had seen their payments delayed because they submitted the wrong bank details, he said.
The popularity of replacement boilers has been driven by the scrappage scheme, and also by the cold winter weather, according to British Gas owner Centrica.
"The number of central heating systems installed was up around 20% on the same period last year, reflecting a more competitively priced product range and benefits from the government's boiler scrappage scheme," the company said in its interim management statement on Monday.
"However, the business experienced additional costs as a result of the higher incidence of boiler breakdown call-outs during the cold weather in the first quarter."
A scheme in Scotland, similar to the English scrappage scheme, will offer £400 vouchers to 5,000 households. It has been unveiled and will be open for applications from 24 May.
In Wales, vouchers worth £500 have been available since 6 April. However, this is only open to those aged 60 and over in order to target those more vulnerable to fuel poverty.