Start with the ordinary user settings
Record the displayed temperature, target, heating mode, fan mode, and active schedule. Check whether a hold ended or the schedule changed the target. Use only ordinary user controls described in the thermostat manual. Do not change installer settings, open the furnace, or move thermostat wires.
Notice whether the equipment stopped after the thermostat said the target was reached or while the display still showed a heat request. Record how far below target the room remained and whether the displayed temperature later changed. A rounded display is useful context, not a precise measurement of the full home.
A light describes a state, not every possible cause
Furnace codes and normal states are model-specific. Daikin's DR96TN instructions, for example, list separate normal states, fault states, and stored-fault functions. That is why the exact manual and history matter. A current normal indicator cannot substitute for investigating the reported event. Daikin DR96TN control and troubleshooting instructions.
Do not reset power to make the light look normal. If a code is safely visible through the usual viewing window, photograph it. Ask the technician whether relevant fault history can be retrieved before anything is cleared.
Ask which link in the chain is failing
If the thermostat is not requesting heat below the intended target, ask for a review of its sensing, settings, schedule, and configuration. If it is requesting heat but the furnace does not respond, ask what prevents the requested operation. If heat runs but the room remains cold, ask how output, airflow, and home need compare.
These are branches for the technician to investigate, not three diagnoses. A heater that stops early, an inaccurate thermostat, and insufficient delivered heat require different evidence and work.
Make the follow-up test match your complaint
If a setting or part is changed, ask what was checked afterward. Did the furnace respond to the intended request? Did it complete the applicable cycle? Does the service record explain the remaining temperature concern?
A repair that makes the furnace start is not necessarily a resolution if it still stops below target. If the event cannot be reproduced, preserve the uncertainty and agree how recurrence will be handled.
Your next step is to share one short sequence record showing the target, displayed temperature, heat-request state, and stop time. Request an explanation of that sequence, rather than treating a normal light as proof the heating problem is resolved.