I have a Potterton combi boiler which has started making some noises. Firstly it makes an intermittent ticking or clicking noise (although could pass as a buzzing noise) after the boiler shuts off following heating water. At first I though this was the boiler cooling down after heating the water but I am not convinced. Secondly it makes a relatively low level hissing noise when the boiler shuts off. Both noises are often heard together and can both be stopped by briefly turning the kitchen cold water tap on, hence why I am not convinced the noises are caused by the boiler cooling down. The central heating and hot water continue to function normally. I have only recently moved into my current flat which I am renting and of course the noises could be normal. Do you think I should contact the letting agent and request a professional takes a look? Any advice will be appreciated.