Our Potterton Promax Combi has started to become very noisy when drawing hot water for a bath. When any other tap is used you can't hear any noise of water going through the pipes, but when drawing hot water for a bath there's a high pitched whooshing sound. Almost like you sometimes get from a tap valve itself, but there is no noise coming from the bath tap - it's definitely in the boiler. Seems to be working fine and as I said no noises when water being drawn from any other tap in the house. Presume it's something to do with there being the most demand when drawing water for a bath, but no idea where it's coming from or how to stop it. Only started doing this recently.
Any ideas?
Any ideas?