honeywell st799

  1. I

    Honeywell ST799 will control HC or HW but not both

    Hello all, I have a rental (gravity system, Baxi bermuda back boiler) on which I have replaced the mid position valve head as it was old and worn out. Testing the system it works as it should, individually. But, If I set the controller to control the system, constant or timed, which ever I...