Salus VS05 Installer's/User's Manual page 18

LED indication in Manual mode
Slide switch "HAND" position to will not follow Group master VS10 and will longer be part of the group.
The VS05 will work as a standalone thermostat
To return the VS05 to the group (if applicable) move the slide switch to 'A' .
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VS05 Installer Manual
RED Led indicates that power is going to
the unit in normal operation. The top LED
will illuminate when room termperature
falls below your required temp.
Green LED means that
the unit is calling for heat.