To dream of something boiling represents turmoil or aggravation. Negative emotions or intentions or worsening. A negative situation may be close to reaching an endpoint. Boiling may also reflect your preparation to release negative emotions or intentions on others. There is potential for anger or revenge. You may also be noticing how negative or dangerous a situation is all the time.
Alternatively, boiling may represent a constant state of readiness or power. Aware of yourself always being ready to take action.
Example: A man dreamed of seeing water boiling on a heater in his bedroom which he walked towards to turn off. In waking life this man was secretly thinking of firing an engineer who was giving him difficulty and at the last minute came to an agreement with the engineer. The boiling water in the bedroom represent the secret aggravated thoughts of the man as he grew closer to firing the engineer.