All of my toilets in the house have started to run intermittently. Is there something wrong with the plumbing or could it be that the flapper has gone bad on all the toilets at the same time?
There's nothing wrong with the plumbing...the flappers do go bad eventually. I h ave an ongoing problem with my 2 toilets. Not that it's really on-going, it's that I put it off until I can't stand it.
Replace one of them (the flapper or the whole kit) and see if the problem is solved (it will be!). I don't have to tell you what to do with the rest of your plumbing if this works.