Questions? comments? suggestions? issues? Close all air bleed valves on your radiators, then close the drainage valve and remove the hose by holding the hose up you will ensure any remaining water drains off. A combi boiler, also known as a combination boiler, provides heat for central heating and domestic hot water upon demand with a combi boiler heating system you do not require feed and expansion tanks in your loft space or a hot water storage cylinder, therefore.