Householders are being urged to avoid a "nasty shock" by checking now whether their insurance covers their heating system as temperatures tumble.
Of 390 home contents insurance policies on the market, only a fifth (21%) include cover for home emergencies, such as a boiler breakdown, as standard, financial information business Defaqto found.
It also said that only a quarter (24%) of the 371 buildings insurance policies on the market provide cover for home emergencies as standard.
Some policies allow customers to add on home emergency cover.
Nearly half of the contents and buildings insurance policies currently available offer home emergency cover as an optional add-on, Defaqto found.
This includes 45% of contents insurance policies and 49% of buildings insurance policies.
Another alternative is to purchase a separate "standalone" home emergency insurance – and there are currently 104 such policies available, Defaqto said.
Home emergency insurance is sometimes added on to home contents and buildings insurance and packaged bank accounts or offered through utility providers, so it is worth checking whether there is already cover in place and checking for any exclusions, before buying a new policy.
"Can be a nasty shock"
Brian Brown, consumer finance expert at Defaqto, said: "As the temperature starts to drop, having hot water and heating becomes a higher priority again.
"Modern boilers are expensive and the cost of having to replace one can be a nasty shock."
Defaqto also said people should bear in mind when choosing a policy that, generally, home emergency insurance offers more comprehensive cover than just a boiler breaking down.
It is designed to help people who have been hit by an emergency to make their home safe again or reinstate essential services – and may also include protection for burst pipes, electrical failures and roof damage caused by the weather.
In some cases, home-owners may find that, with home emergency insurance, they will be covered for alternative accommodation if their property is uninhabitable for a while.
Boiler breakdown insurance, meanwhile, is specifically designed to protect against future costs of a boiler breaking down. A large proportion of policies include an annual boiler service.
There will also be exclusions in some policies however, based on the age and power output of the boiler.