My basin taps do this sometimes. I turn the bath taps on and I hear whooshing behind me and the other taps have come on. It doesn't happen all the time I usually mutter about the DC not turning them off fully, but it has only happened since we had a new boiler fitted November 19.
No help, but it would be good if anyone else could explain why.
I've had new washers put on my bath mixer tap but when the boiler comes on to make hot water, the bath mixer starts dripping fast. I have to go and turn it off very tightly. I don't understand what's happening. The bath mixer doesn't drip otherwise. Any idea what's going on? When I've felt the dripping water, it's cold not hot..