Pipe Flow Module - Coupling Heat Transfer Between Two Pipes

Hello,

I am using the Pipe Flow Module to model heat transfer between to concentric pipes. Two pipes with water in them and 0.8 mm of steel between them. I am using a Wall Heat Transfer condition in each pipe to couple the pipes. I need help in properly setting up the Wall Heat Transfer settings.

I've set variable "T1" as the external wall temperature for both walls, but that does not seem to work. The simulation crashes with:

Undefined variable.
- Variable: T1
- Geometry: geom1
- Boundary: 1
Failed to evaluate variable.
- Variable: comp1.nipfl.wht1.Text
- Defined as: T1*unit_K_cf

Could someone take a quick look at my settings and tell me what I'm doing wrong? Thanks!