I am hoping someone can help..? My Vailant Ecomax combi bolier kettles when the hot water comes on, on the timer or when we run a bath/shower. It only comes on with the hot water, not the central heating. When it starts making the noise, I can make it stop by turning the heating on with the thermostat (turning it on to trigger the heating coming on). The noise will stop within within about 10-20 seconds and then I can turn the thermostat back down again and it stays quiet. I have already added boiler noise reducer to the central heating, but this has not helped with the noisy hot water. I have also had the heat exchanger replaced with a new one (the old one was quite blocked). Can anyone tell me how to fix this?