I used to just keep putting DS back to bed, & he was going ok. Sleeping all night in his bed (usually falling asleep in mine first).
Then its started to get colder. He's not a fan of wearing clothes to bed. I can force him sometimes, but if he really wants to, he can strip himself He's also not a blanket fan. So he was kicking the blankets off (dressed or not) & waking up cold, so would come to my bed. Himself or yelling out, depending on his mood.
The last few nights he's been ok again, not waking, so I assume its coz he's been warm enough.

But, you say you have an electric blanket on the bed, so I guess its not the cold... Have you tried laying with him in his bed till he falls back asleep. I know how hard that is when you could just let him in & sleep again, or if you are feeding a baby, but it might be worth a try. He might get it that he needs to stay in his bed & won't be let into yours if you stop giving in?