U4 - 3 red flashes, 5 green flashes — Outdoor thermistor fault

What does U4 mean?

This fault indicates a problem with an outdoor thermistor (specific sensor not detailed here, but likely related to ambient or operational temperature).

• Faulty outdoor thermistor
• Thermistor disconnected
• Open or short circuit in the thermistor wiring

Click steps to track your progress.

1. 1

   Check the connection of the relevant outdoor thermistor.

2. 2

   Inspect the wiring for damage or loose connections.

3. 3

   Test the thermistor's resistance.

4. 4

   Replace the thermistor if it is faulty.