Just returned with a new passport and now need to get extension transferred. Anyone know if there is a time limit for this job or a fee involved?

Go to immigrations with the form : http://www.thaivisa.com/forum/files/file/20-transfer-stamp-to-a-new-passport-form/

and photocopies of: old passport ID, the visa you last used to enter, extensions, re-entry permit and of new passport ID page and both passports.

Some offices will want a letter from your embassy as well. The US embassy automatically issues you the letter when you collect the new passport. Others I think you have to request it.

There's no official charge. I had mine down at Jomtien without charge.

Not sure if there's a specific deadline, but if you go in for 90 day report or anything else with immigrations they'd probably tell you that you need to do the transfer first since they wouldn't be able to process you using the new unregistered passport or the old cancelled passport.

Thanks very much Suradit69, most useful. Much more complicated than i hoped but hey...this is Thailand !

At least for the UK once you get a new passport your old one is invalid