Some of you followed my post a few days ago about our new boiler and my concerns about the adequacy of the water heating. Ever since the boiler was installed along with a new HW primary circuit on a Y plan, we have been concerned about its performance. In answer to those who say "Get the plumber back" - yes, he will come back at a moment's notice but this week he's away on holiday. What concerns me is that I can hear a gentle trickling sound inside the cylinder. The first time the plumber came back he fitted a vent on the flow pipe beside the cylinder and got a lot of air out of the coil. Now why would I still be able to hear a trickling sound? If there was air in the coil and water was trickling past it, surely that air would have risen to the top of the coil and up to the vent by now? There's another strange symptom: when you draw off hot water the cold supply pipe entering the bottom of the cylinder from the F&E tank becomes cold very quickly as you would expect. The boiler fires up as you would expect. As soon as you stop drawing off hot water both the cold supply pipe and the cylinder vent pipe, rising straight from the top of the cylinder, become very hot very quickly. Now I know water expands as it warms up but this seems remarkably sudden. The plumber did ask me to check that the pump isn't pumping over and this morning I went up and checked again while the boiler was firing and saw no evidence of hot water flowing over the top and back into the F&E tank. Is it possible that while doing the work on the primary circuit the plumber may have indavertantly ruptured the coil? There's never been any smell of Fernox (a distinctive alcohol-y smell) in the hot water and there's absolutely no other evidence of the pump pressurising the cylinder or any contamination with primary water. The HW cylinder is 20 years old - how common is a ruptured coil, in your experience? Surely if this had hapened due to a mechanical twisting force being exerted on the outside of a union, there would also be a leak outside the cylinder? We will get the plumber back next week but as always I'm grateful for your thoughts.