The special £25 payments are paid out when the winter temperature is below zero degrees for seven consecutive days, meaning large parts of the greater Bristol area have now qualified.
But payments are only made to those who receive a qualifying benefit and in the case of those over pension age, that means those who get pension credit.
But Government figures show around one in three of all pensioners who are poor enough to receive the payment do not take it up.
Northavon MP Steve Webb said as a result, not only do they miss out on weekly help through the pension credit system, they also do not qualify for cold weather payments.
Based on Department for Work and Pensions figures for the 10 constituencies in the West of England area, the Liberal Democrat MP has calculated that around 25,000 older people on a low income will miss out on extra help with heating costs due to the current cold weather.
He is now calling on the Government to mount an urgent take-up campaign to make sure pensioners get the money they are entitled to, as well as changing the rules to allow cold weather payments to be made to all those in need.
Mr Webb said: "It is shocking that thousands of vulnerable pensioners in the West are set to miss out on help with their heating costs in this cold spell.
"Many pensioners could get help through pension credit but do not take up that help because the system is so complex and off-putting or because they simply do not know they are eligible.
"This means they also miss out on the extra help they need through the cold weather payments that have been triggered across much of our area.
"The Government must urgently identify those pensioners who are missing out and make sure they get all the help they are entitled to as a matter of urgency.
"They should also look at changing the rules to ensure that help gets to all those in need, regardless of whether or not they are claiming a particular benefit."
Mr Webb said there were currently 49,300 pensioners in the West of England area, which includes all the Bristol parliamentary constituencies, Northavon, Kingswood, Wansdyke, Bath, Woodspring and Weston-super-Mare.
National figures show that for every two pensioners on pension credit, there is another one who is entitled but does not receive it. That means about 24,650 OAPs are missing out.
People can log onto http://pensions.direct.gov.uk/en/cold-weather-payment/home.asp and enter their postcode to find out if a particular area is covered by cold weather payments.