toilet won't refill if washer or dishwasher is on

[JimAtlanta]

the toilet won't refill if the washer or dishwasher is using water. once their demand stops it will refill.
how do i fix it? i replaced the entire refill valve with fluidmaster.

[Spunkmeyer]

Sounds like a water pressure issue more than anything else. I'm not sure anything other than a larger water line would take care of that.