It is quite confusing when you have a new passport and a valid visa on the old one. It is advised that you contact the Thai Embassy in your country before you travel. Often the answer is carry both the passports. In case the Passport is an Indian one, The immigration at the Indian airports may ask for the employment contract and wp3 form before they let you board the flight. Please ensure that there is no ECR (emigration check required) stamped on your passport. If that is the case then get a new booklet without an ECR stamp. ECR is stamped if you have not submitted your 10th class certificate or Pan card while applying for the passport. Many countries would deem an old passport invalid the moment you apply for a new one. If you have a NON B Thai Visa, I suggest you check with the Thai embassy in your country before leaving. For Tourists, this may not be an issue.
Leave a comment and let us know if you have had such an experience.