Hi, I've just had a Vaillant EcoTec Plus 832 fitted. Whenever it switches between Central Heating and Hot Water, the diverter valve has a loud buzz to it. I've never heard a combi boiler so loud when switching (you can here it from upstairs). Has anyone else seen/heard of this issue? Not sure whether it's a faulty part or it's the normal with this type of boiler. Would post a video if I could but it's oddly Loud.