Hi, some years ago I had a PCB replaced after a failure of the system i.e a loud buzzing was coming from the cylinders control panel. about 8 weeks ago the buzzing returned briefly but after a few weeks stopped. Now it seems that often the hot water is not as hot as before and if you use the shower it runs out quickly. I hava a suspicion that the heat generator pump is continuing to run for hours after the boiler stops and the heat is beiing lost through the heat exchanger in the Potterton heat generator which is in the garage. Has any body else had this problem?