Your boiler should be covered if you have home insurance that includes home emergency cover as standard. If not, home emergency cover can be added as an optional extra to your home insurance policy or bought as a standalone policy.
While home emergency cover might not be boiler-specific, it will typically cover 24/7 emergency call-out fees and repair costs if your boiler breaks down. If you want more comprehensive and specific cover for your boiler, you might be better off with dedicated boiler cover.