Molar had root canaled through crown by making whole.it is sealed with composite.feel hot and cold, but painless. is it ok as long as, don't have a pain?

Depends: It depends on how long ago you have had the root canal therapy? Sometimes, a tooth is still sensitive for a while after the treatment. You should consult with your dentist to address the problem.

Clarification: When root canal therapy is completed, as it seems to have been done in your case, you can no longer feel cold and hot sensations from that tooth. There is no longer any nerve tissue in that tooth to transmit these sensations. If you still feel cold and hot sensitivity, it is coming from another tooth. No pain is good. Feeling hot and cold from teeth is normal if not severe or long lasting.

Yes: As long as you don't have pain or swelling, you should be okay. The dentist will typically follow up with you to make sure the root canal looks good after a year.