I have a push button Cistern flusher on top of the cistern and the plastic water filling gadgets inside the cistern have clogged up with Limescale leading to the valves not closing tight and the cistern overfilling. a) can this be used in cold water or would it need hot? b) is this product suitable or should I use something else? I'm no plumber although I don't mind taking things apart to clean them, trouble is anything I touch attached to water seems to end up flooding somewhere so some kind of cleaner which doesn't require dismantling the contents of the cistern is preferable. Thanks