When it gets really cold outside, our hot water freezes in part of the house. I've installed foam board, insulation around the pipes, everything I can think of. It seems to freeze right at the metal elbow. Our pipes are mainly plastic but the elbows are metal. What else can I do to prevent this from happening every year?

Thanks so much.

Heating tape,

https://www.acehardware.com/departments/heating-and-cooling/heaters/heating-cables

Assume you are already doing this, but be sure to leave a little water running, especially on the hot side in your case.