We developed a leak detector based on pressure change measurement using a leak-tight master and test chamber, modeled the system and simulated the pressure responses. As the heat transfer tend to be different between master and test chamber, imbalance of temperature recovery will occur when the required temperature recovery time is not satisfied and produce unexpected pressure difference despite leak tight. This will increase the inaccuracy of the leak detector. The mathematical model was established and the heat transfer coefficient of the master is set to be slightly different with the test chamber to show the phenomena. The results showed that inadequate temperature recovery time produces unexpected pressure difference and reduce the accuracy. The results were verified experimentally and showed a good agreement.