What are signs that a root canal is going bad?

Inflammed or infecte: Also may mean sensitivity to heat or cold, which is indicative of a possible root canal problem. Several previous answers on this topic should be reviewed.

A sore on the gum: Root canals can fail for many reasons including fractures of the tooth or the bacteria getting into the filling material that fills the space previously occupied by the nerve of the tooth. A sign of failure can be a sore in the gum- not too far from the tip of the tooths root - often with pus coming out of it.

Pain: If you've had a root canal and the tooth is still causing you pain, then the root canal may be failing, the tooth may be infected again, some of the necrotic nerve tissue may not have been completely cleaned out, or the tooth is cracked. Waiting for a draining fistula to occur is not absolutely necessary. But if one occurs, there's a good chance that it's either endo, perio involved, or both.