I have a mixing control and it shows a mixing demand but it will not open the mixing valve or the variable speed injection pump.

Mixing controls are designed to provide boiler return protection. On the control display, check the boiler temperature measurement in the View menu. Then enter the Adjust menu and check the BOILER MIN setting. If the measured boiler temperature is below the boiler minimum setting, the mixing control is designed to close the mixing valve or reduce the speed of the variable speed injection pump.