close coupled wc in a house 5 to 10 years old.the fill in valve is a fluidmaster 45, the grey top one. it works when the wc is flushed and refills to the set level.
however two feet away are the bath taps and when the hot or cold or both are turned on the cistern fills through the fluidmaster and overflows.when the taps are turned off the cistern continues to overflow and will only stop when it is flushed.
i have a new replacement fill in valve of the same make to fit but can anyone suggest why its happening please