For days the c/h works fine and is very quiet except for kettling noises from boiler. A new pump was fitted last year after the old one went bang. However, I am now hearing the most horrible rumbling noise as water/steam seams to charge through the pipes in the airing cupboard and up into the header tank (the small tank in the loft). The header then fills up rapidly with super hot water and then there is a bang like a water hammer effect and everything goes quiet - sometimes for just a few minutes like today (its very windy outside ???) - sometimes for several days. The noise sounds very bad, I feel like something is going to burst soon!!