Safety: Isolate power before working on wiring. Use appropriate ladders and fall protection when accessing outdoor sensors.

Step 1 – Visual inspection:
- Locate the Protherm outdoor sensor on the north or shaded wall.
- Check for physical damage, paint over the sensor, or water ingress.
Step 2 – Check connections:
- Open any external junction box.
- Ensure sensor wires are firmly connected and not corroded.
- Clean terminals and re-tighten.
Step 3 – Measure resistance:
- Disconnect sensor wires at the thermostat or junction box.
- Measure resistance with a multimeter.
- Compare to Protherm outdoor sensor resistance chart.
- Open circuit or near-zero resistance indicates a faulty sensor or cable.
Step 4 – Replace outdoor sensor:
- Install a new Protherm outdoor temperature sensor.
- Seal cable entries to prevent water ingress.
- Route cable away from high-voltage lines.
Step 5 – Verify configuration:
- In thermostat installer menu, ensure Outdoor sensor is enabled and correct type is selected.
- Restore power and confirm F7 is cleared and outdoor temperature is reasonable.

F7 error and thermostat shows unrealistic external temperature or cannot read outdoor sensor.

Possible Causes