You could have an older grey control box, which is why I asked if it was clear. I am not sure how the old grey ones work exactly. For the clear ones when you call for heat it should not blink blue, only when power is restored to the unit. When you call for heat there will be a red call for heat light usually on the outside of the unit. The control box will first light up green (solid) then eventually go to red (solid). The only blinking is either the blue status light only at initial power up, or an error code.