My system goes: Tank with heat exchanger ->HIH->FPHE->filter with coolant hose wrap->temp sensor->IP
I believe the gauge is working because it did register slightly. I also touched the sender wire to ground and it pegged the gauge. I don't know anybody with a non-contact thermometer to borrow. All of my heating lines seem to be getting hot, as does the FPHE. The line from the FPHE to the filter also seemed warm, but the output from the filter did not. I am hopeful that switching the FHPE and Filter will give better temperatures.