Replaced a lever type t/stat (heating & A/C) which had 5 wires connected.
Orange wire > yellow terminal on T/stat
White wire > terminal
Green wire >terminal
Red wire >terminal
Black > terminal.
The new Noma has 4 terminals only Yellow, White, Green & Red. Connected and matched
Colours using Orange to yellow. Seems to work OK on heat control with black not connected anywhere. (No A/C unit as yet) Anyone know the use of the black wire on lever type? Any potential problems with this wiring as done?

The black may have been a common. For heat only, all you need is the red and white. If the thermostat has a fan on option, you will need the green.

Thanks. I suppose this means that the Noma uses its own battery supply (2xAA) for its display and electronics. Thanks again.