Hoping someone might know how to fix this as it's getting on my nerves! Old style boiler with water tank (not combi) started whistling yesterday when I happened to switch the water on to heat at exactly the same moment as DH flushed the upstairs toilet. Google tells me it's probably air in the system and I'm assuming that happened because the water flow was reduced (by the toilet refilling) at the moment the boiler tried to start pulling in water, but it doesn't tell me how to release said air. Can call HA for a repair if absolutely necessary but it's like pulling teeth trying to get an appointment so if it's a quick, simple fix it's easier to do it myself, just need to know how!