Hi, just wanted to add to this, because my DS1 was unable to stay dry at nights until he was 7. I'd done the lifting, and also gritted my teeth for 4/5 weeks at a time before going back to night-time nappies. One of the problems was definitely that he is a very very sound sleeper. And we tried star charts, lots of praise, no negative comments.....
We got to see the incontinence advisor just before his 7th birthday. She advised making sure he drinks plenty during the day, and also goes to the loo several times, to get his body/brain used to the sensation of being "full" and "emptied". But no drinks from the hour before bedtime, and keep a record of what the last drink was, in case a pattern emerged. And she involved him, asked him how he felt about it, explained how his body worked etc. And we were loaned an alarm, (which generally fell off/didn't work, but at least helped focus his mind). We also had to keep a record of what time he wet (often dry when I checked at night and was wet first thing in the morning, which apparantly showed that he could hold on to wee!).
And the other important thing was, there was no going back to night-time pants. It took about 3 months. (in winter, too, with hindsight not the best of times....)
She warned they often relapse for a while about a year later, but that's not happened. It did take time, and he did sleep in wet beds (so soundly, don't think he was too bothered!) but I have also heard something about not always being physically able to be ready until they are 6/7 sometimes.
Hope that some of this helps, good luck!