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. Are there any downfalls to combi boilers? We are still gathering data for this location try changing location above or. Didn't unblock sink at all,if anything is was more blocked after applications, even when left for hours! Ruling in pimlico plumbers case will set.