This is an effective way to make sure your sink remains unblocked, which you should repeat once a month this video shows you how. Leave a rating for your tradesperson based on quality, reliablity and value. Worcester combi central heating boiler in good working order its 5 years old and has been regularly serviced. Sink blockages: try using a drain snake to push, break up, or remove the blockage. The ecoblue heat and the advance heat are comprised of 5 sizes each; from 12 to 24 kw, and from.