DPT 20.102 (HVAC Mode) encodes the four standard modes - Comfort (1), Standby (2), Economy (3) and Building Protection (4) - and is applied as a cascade from the currently active mode.

The four modes form a hierarchy ranked by comfort/economy. Comfort uses the full occupant setpoint; Standby applies a small offset (deltaT of 2-4 degrees C) for short absences; Economy applies a larger offset (deltaT of 4-6 degrees C) for long absences and night-time; Building Protection enforces a safety setpoint (frost protection or overheat protection). The DPT 20.102 value is carried as a single byte in the telegram.

Always confirm that Building Protection (mode 4) is wired and tested first: it is the only mode that prevents real damage (freezing pipes, overheating equipment) when everything else fails.