Did you know that improper sizing of your boiler can make your unit run less efficiently and wear out prematurely? Find out what central heating systems are available with this guide from uswitch decide what type of central heating system is best for your home. Why, a plumber would be ashamed to take as long as that over a job! Valid on natural gas boilers only. With no water tank to heat up, combi boilers can provide an unlimited supply of hot.