Plumbing

FOGHORN when drawing hot water but only after the water tank has been heated.

Anonymous user 03/03/2024 - 3.32 PM

I have actually asked this question before, about 3 years ago I think. Unfortunately the problem has re-occured but I think this may go some way to help a professional come up with the reason; My set up is as follows...a very large water tank in the airing cupboard with white expansion vessel above but no cold water header tank. I think it's called a mains pressure unvented cylinder?? The last time it started was just after I had the expansion tank replaced because it started leaking. I called the plumber back but he fixed it while I was not present but my wife 'thinks' he said he had to reduce the pressure. I assume this was the pressure in the new expansion vessel. Whatever, it fixed the foghorn. About a month ago the replacement expansion tank was found to be leaking. A different plumber was called and fitted another new expansion tank. Yet again, a week or two after that we started getting the foghorn again! Interestingly, the foghorn only happens on the first draw of hot water after the water has been heated. If the timer is set to heat the hot water at 8pm, the foghorn only happens when drawing water when we retire to bed. If I set it to heat the water at 8am, the foghorn will occur on the first draw of hot water after that, whether it be at 10am or later in the afternoon. I called this plumber back but he said it was just all coincidental. He said he had set the pressure in the expansion vessel to the manufacturers recommendations. He did also mention something about a 2 or 3 way valve that has been fitted down near the floor should really have been located up higher much nearer to the expansion vessel and that these can fail. So my questions are: 1. Why would the second expansion vessel start leaking after only 3 years? 2. What is causing the systen to make this noise. It surely must be pressure related as it only occurs after the water is heated and I am assuming that the first draw of hot water is releasing some pressure from the system. Thank you in advance.