We have an Ideal Response 100 combi boiler. For a while now, after the central heating has been on five minutes (and the pressure gauge has gone up approx 0.2), the boiler whistles for about five minutes and then stops. It then whistles for a few seconds immediately after the ignition has fired up again . The whistling has now got a worse - louder, almost a squeaking sound. Any ideas what is cause be?
