Hello! I have a question, I had my heating on earlier today (around 1pm for an hour) and no noise, I ran a bath at around 7pm, and (turning taps on and off to make sure) had this loud whistling sound coming from the boiler when the taps were on. From what I can see, on the front cover, I have a "Potterton Promax Combi HE Plus." Could anyone tell me what this could be? Had it fitted new Jan 2014.