Symptom
User interface has no display and Quantum is cold

Check: There is power to the peak circuit and that the off peak supply circuit breaker is on or fuse for that circuit intact.

Check: Both the peak and off peak switches are in the On position. if not then switch both on.

Check: The peak mains supply is present at the Quantum  mains input terminal block, terminals 3 and 4 (counting from the left) 3 being L and 4 being N (this is fed from the mains filter board, located behind the CC). If no supply is present at the CC and there is power to the mains filter, then replace the mains filter board.

Check: Connection between the UI and CC is in place at both ends and undamaged. if not terminate correctly or replace damaged part.

Check: That 12VDC is present on the lead from the CC to the UI, whereas red is +ve and black is –ve.

Swap over UI and see if fault clears, if so the fault is with the UI, If not put the original part back.

Swap over CC and see if fault clears, if so the fault is with the CC, if not put the original part back.