F5
Ideal
Outdoor Temperature Sensor Fault
F5 displayed and thermostat cannot detect external temperature for weather compensation
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed external outdoor sensor, Open or shorted sensor cable, Incorrect sensor type fitted, Loose terminals at thermostat or wiring centre
How to Fix / Troubleshooting
Safety first: Turn off power to the heating controls before working on wiring.
Steps:
- 1. Locate the outdoor sensor: Typically mounted on a north or north‑west facing wall away from direct sun. Inspect for physical damage, paint over the sensor, or water ingress.
- 2. Check cable and terminations: Follow the cable back to the thermostat or wiring centre. Tighten terminal screws and ensure the cable sheath is intact with no crush points.
- 3. Measure sensor resistance: With power off, disconnect the sensor and measure resistance. Compare to Ideal's specified NTC curve (e.g. around 10kΩ at 25°C if using a 10k NTC). A reading of 0 Ω or infinite indicates a faulty sensor or cable.
- 4. Replace sensor if faulty: Fit a genuine Ideal‑compatible outdoor sensor, observing polarity if specified. Route the cable away from mains cables to reduce interference.
- 5. Reconfigure thermostat: In the thermostat settings, ensure 'Outdoor sensor' or 'Weather compensation' is enabled and the correct sensor type is selected.
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Repair Difficulty
Medium
3/5
Required Part
Ideal Outdoor Temperature Sensor
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