Came out today to inspect a runaway heat pump that is only heating on aux heat. Payne air handler model #pf1mnc031, serial #2406a71335. Upon arrival I called for heat to test the system. I observed the system start and go directly to aux heat. I powered it down waited and called for ac. The system started normally and has a temp split of 18°. I powered it back down waited and called for heat again. The system still went directly to aux heat. I traced the control voltage and found a bad relay. Normally I would just try to replace the relay however this relay has a board attached to it. This is a specific part that would need to be ordered. Once the repair is made further diagnostics may be needed.