Grundfos Miximizer

I have a grundofs miximizer UP 15-42 FC/MR on my in radiant floor heating system. It's approximately 18 years old. Four days ago on a cold long weekend in February the miximizer stopped circulating water. All 4 lights are lit up (not blinking). There is nothing in the troubleshooting section of the manual that details this.
When I cycle the power on the furnace and leave the furnace off for more than 4 minutes the pump will circulate with the proper lights blinking for approximately 8 minutes and then all the lights will light up solid and it will stop circulating. It will not correct itself until I cycle the power. I have never had this issue before. I'm trying to determine if its a mechanical issue or electrical in the pump. Does anyone know if there is a thermal overlaod.? is it repairable or am I in search of a new pump.