In an isolated system, the total heat given off by warmer substances equals the total heat energy gained by cooler substances. What might have caused the difference you have reported?

Answer: (1) temperature difference between the warm and cold substances

(2) no heat is lost to the surrounding

(3) no heat is gain from the surrounding

Explanation:

Since it's an isolated system,

No heat is transfer in or out of the system. So the system maintain its heat without heat loss to or gain from the surrounding.

The heat transfer is aided by temperature difference between the substances.

According to the law of conservation of energy, the heat loss by a warm object in an isolated system is equal to the heat gain by cold body.