Here I had the water line that came to the house that was too thin to heat.
Also I had a pipe that was in an impossible place to heat with an iron or torch.
In both cases I used a (loctite?) epoxy product that they use for new installations on copper. Thing is once it sets heating does not loosen it so its a one time deal.
Did it as a temporary measure to get water back into the house five years ago.. still holding.