Hi. I am just after a bit of advise. Our boiler, which is an Icos Ideal HE12, makes a noise whenever the water is heating up. At the mo we don't have our CH switched on. The noise sounds like water travelling through the pipes, like a gushing sound. It happens when the boiler comes on in the morning, and seems to be pretty constant until the boiler switches itself off. Has anyone got any suggestions on what this could be, or how I could fix myself? Thanks!