toilet tank fills only when other water is turned on

[gregorymi]

All of a sudden my toilet tank only fills up if I turn on the sink/shower water for just a second. I am guessing there is some sort of bubble thing going on. Any ideas? If it matters this is in an upstairs bathroom. Nothing was recently done at the house with the water or plumbing.

 

[Proff]

It sounds very much like a partial 'air-lock'. You need to know whether the cold water to the bathroom is either direct or indirect and then set about blasting the air-lock out.

Second thought, Is the float valve a Torbeque, If so it just may be sticking and needs the reduction in pressure (turning tap on) to release itself.